JULY,1931 MONTHLY WEATHER REVIEW 277 From a consideration of the mode of formation of cold cipal axis causes dissolution of horizontal inversion zone8 air and warm air masses it could be espected that a posi- while contraction brings sharpening. tive difference between air and sea temperatures corre- A 2-dimensional half deformation field with one hori- sponds to drizzle and a negatii-e difference to shower air. zontal axis and an axis directed obliquely upward causes The author has investigated this rule from 620 observa- frontogenesis and dissolution of inversions. Contraction tions taken at Thorshavn and found that the rule holds along the horizontal axis causes front,olysis, while expan- good without exception for differences greater than 0.5O sion causes inversion formation. C. For smaller differences no definite contradiction The choice of entropy surfaces as equiscalar surfaces could be established. It thus follows that accurate presupposes advective frontogenesis. Thus from the measurements of air and sea temperatures at all inter- beginning the entropy surfaces are inclined and advection national island and ship stations and their report to l/lOo comprises a permanent deforination-field of which the C. or 1/5O F. have great importance for practical weather axis of contraction can not be directly vertical. It thus analysis. follows, as has been previously pointed out, that in the The investigations of the author on horizontal visibil- warm air mass where the isentropic surfaces are almost ity in Scandinavia confirmed the hypothesis that the horizontal almost no frontogenesis occurs; in the cold opalescent turbidity of the warm air mass is notably mass where they are somewhat inclined, weak fronto- greater than of the cold air mass. genesis; and in frontal zones where they are considerably From a previous work of the author (Wellen und Wir- inclined there is effective frontogenesis. bel, Leipzig, 1924) it is known that surfaces of equal The general circulation of the earth's atmosphere is entropy (isentropic surfaces) of the cold mass are inclined divided into several partial circulations. They can be upward toward the pole, while in the warm air mass considered as a system of vertical wheels and of hori- they are almost horizontal. Thus is follows, as is later zontal wheels. The hyperbolic points between the discussed in detail, that the cold mass easily becomes wheels are the centers of the deformation fields in the heterogeneous while the warm air mass with horizontal foregoing sense. Frontogenesis and frontolysis develop isentropic surfaces is among the most homogeneous in the areas between the parts of the general circulation. masses of the atmosphere. The effect of the vertical wheels and horizontal wheels By means of aerological data from Holland and Spieg- will alternately strengthen and oppose each other. litzer, Schneeberg, the existence of at least two separate When the general circulation works frontogenetically, . air niasses is statistically indicated. The potential tem- areas occur where by preference fronts are formed. The perature has at any level two pronounced frequency favored frontal zones run east and west. In the inter- maxima which correspond to polar air and tropical air. mediate zone where the vertical opposes the horizontal When two air ninsses eRch uniformly homogeneous circulation, the resulting effect will be mostly fronto- approach each other nearer than about 1,000 kilometers, lysis so that the air exchange between pole and Equator the area between them no longer fulfills the conditions of n can go on unhindered. homogeneous air mass. A frontnl zone occurs which can Doctor Bergeron's book is conceived as the principle gradually sharpen to a front. Fronts are narrnw inclined introduction to the problem of air masses and front transition zones of the same vertical extent as the air formation. The use of the results for investigating the masses. It is essential that the difference of the values relations actually occurring in the troposphere will be on both sides of the front of at least one of the independent shown in Part 11. The wish may be expressed that we elements (temperature, pressure, wind, humidity) is so may not need to wait long for this continuation. great that it has an appreciable effect on the great scale dynamics (of the air mass). ON PERIODICITY IN SERIES OF RELATED TERMS In the troposphere, fronts are continuously produced and destroyed. The author has called these processes By SIR GILBERTWALKER, F. R. 5. frontogenesis and frontolysis. Kinematic frontogenesis SUMMARY consists in the coming together of the equiscalar surfaces of an element through the motion of the individual In 1927 Tule developed the idea that a series of num- particles. bers ul, uz,. , 11, espressing the condition of a physical In dealing with air masses which are not too extended system, such as successive annual sun-spot numbers, the field of movement can be treated as linear. The might be regarded as due to a series of accidental disturb- movement itself may be resolved into four partial fields ances from outside operating on some dynamical system consisting of a translation, a rotation, an espanaion, and a with a period or periods of its own, probably subject to deformation. Only through the deformation movement damping. The consequent, oscillatioiis would vary both can two particles essentially approach or separate from in amplitude and in period. In this paper it is shown one another. that if Yule's equation defining the relationship between As no essential change of volume can occur, a deforma- successive undisturbed terms of the 11 series is tion is undergone either as an extension along the prin- cipal axis and a contraction along both secondary axis or u"=gIU,-1 fgzu,-,+. .+g*u+-,, as a contraction along the principal axis and an exten- then, provided n is large, a similar equation holds very sion along the secondary &XIS. Material particles which approximately between successive values of rp, the cor- at one time form a plane surface will always form a plane relation coefficient between terms of u separated by p surface which during movement alter only their orienta- intervals, i. e., tion and their distance from the field's center. In a 2-dimensional field the surfaces rotate so that they will r, =gIr+-l + gZT,-2$ . +gar+-,. ultimately be perpendicular to the axis of greatest con- ~ ~~ ~~~~ 1 On periodicities in series of related terms, Proc. Roy. Roc. Series A. vol. 131, No. 818. traction. pp. 518-532. A symmetrical deformation field with vertical axis The subject is treated from tho mathematiral viewpoint and since noone's views are entitled to greater consideration than those of Sir Gilbert we print in his own words the produces the following effects-the extension of the prin- summary of his conc1uuions.-ED. Unauthenticated | Downloaded 09/26/21 12:38 PM UTC 278 MONTHLY WEATHER REVIEW JULY,1931 Thus the graph expressing the r is, which is much smoother each month. These ascents though few in number serve than that of the u's, may be used to read off the character to indicate the direction and force of the winter monsoon of the natural periods of the u's; further various relation- winds along the China coast. As might be expecked ships are found between the amplitude of the c.orrespond- these winds are due essentially to the presenc,e and the ing terms in the Fourier periods and those of the correla- intensity of the so-called Siberian cold season anticyclone; tion coescients. the c,enter of whic.h may be over the Province of Shantung The analysis is illustrated by applying it to t'he quarterly in China, rather than in Siberia. Father Gherzi con- values of pressure at Port Darwin, a key center of world cludes that for winter monsoon days the winds aloft weather, which proves to have a strong persistence and to back with increase in altitude above the surface. Dat,a show evidence of not very strongly developed periods of for the summer monsoon are much too few to permit the about 34%months and of about four times this length or drawing of definite conclusions. Conditions during the 11%years; the series of data is not long enough to settle summer monsoon are much less ready than during the whether the former oscillations are damped and are free winter monsoon. oscillations, but the latter appear to be imposed from The statistical data of surface winds are given in very without and are presumably solar in origin. great deatil for a number of stations on the China coast. The 240 quarto pages c.0mprise.din the report are mostly WULF AND MELVIN ON THE EFFECT OF TEMPERATURE t,aken up with data of cloud moveme,nt and surfac.e air UPON THE ULTRA-VIOLET BAND SPECTRUM OF OZONE AND THE STRUCTURE OF THIS SPECTRUM mownient printed in detail for a number of years of record. Appropriate charts and diagrams add to the The ultra-violet absorption of ozone in the region int,e.rpre.t,ationof the statistics. The price of the work 3400-2300 A consists of a large number of bands appear- is $4.50.--A. J. Henry. ing against a background of continuous absorption. The effeck of temperature upon this spectrum has been studied RESULTS OF RAINFALL OBSERVATIONS IN WESTERN over the range - 78' to 250' C. A definite though small AUSTRALIA effect has been observed. Grossly it manifests itself as The present voluine is the fifth of a series published by an increase in contrast with decreasing temperature. the bureau. Volumes €or Victoria (1910)) N. S. Wales Photometric results show this to be chie.fly a decrease in (1914)) Queen Island and South Pacific (1913), South - absorption between the band edges,.