1'70 MONTHLY WEATHER REVIEW. APRIL, 1915

(49) Khnh& Rubach. Phys..Ztschr., 1913. KSrm6n. G6ttinger Nachnchten, 1911. (50) Ftlppl, L. Milnchener Sitzungsber., 1913, Hft. 1. [A formation of two vorticxs mth a symmetncal body of practically any ehape.] See._ Lanchester.~- Aerodvnamics. D. 39. (51) Lamb. Hydrodinamics,' i.217. (52) Helmholtz. Berlin Sitzungsb., 1888, p. 647-663; 1889, p. 761- ;SO. Tncnslatedin Abbe. Mechanics of the earth's atmosphere,- .- IIIl, - \.STHshington, 1S91, . 78-111. (53) Rayleigh. 'fheory of sound, v. 2, p. 382. (54)Exner. Wiener Berichte, 1911, p. 1411. t55) Margules. On the ene y of stornls. ltanslated iir Abbe. hlwhanics of the earth's etmosf;ghere, 111, Washington, 1910, p. 533- 595, and abstracted in this REVIEW.23:519. (56) For instance, Bee the United States Weather map of the Northern Hwnisphcre, Washington, D. C., Jan. 8, 1914. (57) Kelvin. Proc. Roy. Irish wad.,1889; Math. and phys. papa, v. 4, p. 2024204. (58) Margules. Meteorologische Zeitschrift, Ham Band, 1907, p. 24% (50) SandsWm. Arkiv f. mat., aatr., och fys., 1912. (60) If the velocity of the air above the surface of discontinuity rela- tive to that below, hm a component directed u ward the intensity of the vortex sheet increases; if, on the other ha$ the relative velocity htlv a component directed downward, the intensity decreaaes. (61) Schmidt. Wiener Berichte, Ha, 1913, 12S:S35-911. For the theory of air waves Hee the discussion in the Report of the British Association, 1908, p. 605-611; also a paper by Lamb. Proc. Roy. sot'., 1911, 64A. (62) See for instance: Hadamard. Propagation des ondes. 1903, cha.nt.._.___r-- --2. Lamb. HydrodynamicM, p. 464. I do not think Lord Rayleigh's objection that the equation of ener y can not be satisfied. is valid when the tangential- velocity tu well as +xe normal velocitv is discontinuous. (63) Shaw, w. N. Forecasting weather, p. 246. (64) Schmidt, W. Meteorologmhe Zeitschrift, 1910, 27:406. See also Lanchester. Aerodonetics, 1910, p. 280. (65) Okada, Y. Tohoku Univ'y sci. reports, June, 1914, 3:169-187. FIG.24.-Map showing the driest months in tho western United States.

.. ! . ' 1 _. '. "! ,e i In Februtwy the rainfall influences begin to weaken along the northwest coast md raininess increases the III. THE DISTRIBUTION OF TEE RAINFALL IN THE OR WESTERN UNITED STATES. eastern slops. By B. C. WALLIS,B. Sc. (Economics), F. R. G. S., I?. S. S. [Dated: North Finchley, England, Feb. 24,1015.1 In this REVIEWfor January, 1915, tlie writer mapped in some detail and discussed the distribution of rainfall intensity in the eastern United States; the present paper is a similar discussion of the rainfall intensity in the western portion of the Republic. The accompanying 13 monthly maps of equipluves (figs. 3 1-43) present a notable regularity almost through- out the year, .y, very wet mea gradually fadcs off into a vtq dry district. The exce tional month is October, when tlie raininess is uniforn y below the average, and tlie elevated lands are wetterY than the lowlands. Tlic second general feature is the absence of very marked raininess or dryness on the mountains the gear. This fact is well way, the West rinfd: (1) The Far with grcut rainfall November to March, i.

In January the equipluves run north and south and raininess drcrcmes steadily eastwards. This montll marks the dinias of the irffluences which cause rain and which axe due, in the main, to the winds from the Pacific ' ocean. FIG.26.-Map showing the wettast months in the western United State&

Unauthenticated | Downloaded 09/26/21 01:41 AM UTC APRIL, 1915. MONTHLY WEATHER REVIEW. 172 In March the northeast increases in wetness and On the other hand, meridian 115O W. divides the the western influences weaken generally. By the month country into two parts which have wet winters and wet of April the influence of the Pacific winds has ceased to summers, respectively (fig. 25). Both these statements roduce a marked intensity of rain and continnntnl in- ignore the small coastal area of New England where the guences-due, in the main, to the “swing of the sun”-- rainfall conditions tend to be unique: Consequently, tend to produce rainiiiess in the arcas niost remote froin the western United States may be divided (fig. 26) into the sea; the area of great rainfd intcnsity is latitude three rainfall areas: (A) the west coast with wet winttm 4Oo-45O N. on the eastern slo es. In May the contincntd in Huenccs cscrt R ninsimum effect in t8hiscentrl area, and the southwwt Gnrner is relatively very dry. The Juno areas of wrtncw mid dr ness lie to the north of those which occur in >In;-. fi July the estreme southmn section of the Mcsican boundary of the Unitcd States, which lics within 3 or 4 degrees of the Tropic of Capricorn, brgins to rspcricncc the northward-moving nrca of heavy rainfall nlwaps mcompanying the “vertiod ” sun. Drynvss prevails

Fro. n.-Annual march of rainfall intensity in rainfall regions Am, AII. and Am. (gee 6g. 28.) and dry summers and a Feat range of raiufrrll intensity: (B) the eastern slopes wlth seasons the reverse of these, andalso a great range.of intensity; and (C) the mountains with indefinite rainfall seasons accompanied by a slight range of intensity, although the cold season tends to be rainier than the warmer half year.

Flo. 28.-Rain(all regions of the western United States. over the western coast lands. In August, .July conditions are continued and develop a more definite dryness in the north. In July and August the Pacific coast lands are marked by an esceptional clrpess (below 10 per cent), being the minimum intensity of rainfall occurring any- where in the United States. In September the sout,hern masirnuin and tho western minimum persist, but in a less marked de-ree. October is a dry month in the United States, an8 it is slightly drier in the West than farther east. In November and December the oceanic influences begin to work toxard their January maximum; they increase in power as the Fro. 28.-Annual mrcb of ralnfall intensit in rsinfall regions Arb, Arrm, and Arrrh. (See I, 26.) winter comes on and as they gradually reach farther southward. In the west coast divisions (fi 27) the oceanic influ- Figures 24. 25, and 36 are based lipon the monthly cncm found on the north gradua7i -y increase in intensity ma s (fi . 31-43). southward. On the other hand, the oceanic influences goy& a line from El Paso to Missoula divides the decrease in intensity with distance from the coast Unite States into two parts having dry winters and dry (fig. Bummers, respectively. 1 Su? thh REVIEW,January, 1915,48: IS, 17, figs. 8 end 10. Unauthenticated | Downloaded 09/26/21 01:41 AM UTC 172 MONTHLY WEATHER REVIEW. APRIL,1915

28). The three areas, for which gener&ed graphs are ing chart of the rainfall regions of the eastern United shown, agree in having increased raininess which prevails States (fig. 8) figwe 26 indicates that the rainfall of the in May in comparison with A ril. This latter fact is of United States as a whole is determined by (1) continental interest in connection with tl e rsininess of the interior influences which we exerted over a broad triangle of of the continent in that month. country with the vertex to the south and with the edge Pigure 30 refers to the eastern slopes and shows how of the hooky Mountains as the easte n limb of the tri- the maximum effect occurs in the center in May, in tho angle; (2) oceanic influenoes exerted upon the coastal north in June, and in the south in July. The period of heavy rains is also shown to be limited in each portion of the area to approximately three month.

I' SONDJFYAMJJASJ FYO.!B.-Amual march of rainfall Intensity in rainfall regions Cr-Crrr. (Sea flg. 26.1

Figure 29 indicates tho details for the mountain &vi- Fie. 8O.-Annusl msrch of rainfall intensity in rainfall regions Bi-Em. (See Ag. 25.) sion intermediate in location and in type of rainfall lowlands, (a) on the west from the Pacific and (6) on the between the other two areas. In each case there is a east from the Atlantic: (3) intermediate regions (a) the double maximum. It is interesting to note that in Rockies in the west and (6) the western A palachians on general the equinoxes are dates when the rainfall inten- the east; and (4) direct solar influences wg zoh are mani- sity tends to ap roach its average and when the periods fest with some elements of variety along the southern of wetness and $nesa, respectively, tend to terminate. boundary as far west as Yuma, biz. The location of these several rainfall re ions are indi- -~ cated in figure 26. In oonjunotion with tfl e correspond- *&e this REVIXW,Jsnuarp, 1915,II: 16,17, figs. 8 and 10.

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Fm. 82.-Equipluves for the weatern United States for February.

FIQ.33.-Equipluves far the western United States lor March. Bla M.-Equipluves for the western United States lor April.

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FIQ.I.-Equipliivw for the weatem United 8trrt.w for June.

FIQ.37.-Equlpluves for the westem United States for Jnly.

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Fro. 39.--Equipluves for the western United States for September. FIQ.IO.--Equiplura~ for the western United States for October.

FIQ.Il.-Equlpluves for the western United States for November. FIG.I?.-Equipluves for the western United States for December. 96342-15-4

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