ATMOSPHERIC TIDES AND OSCILLATIONS 
517 
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FRANCISCOUF SD - CITY | D WASHINGTON D 
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t \ 
AAMT. WILSON | de 
GALVESTON If D r\ 
in NEW ORLEANSW ~~, 
20 KILOMETERS e \ 
0 500 1000 1500 1 J 
a ———— eel 
E D 
52 \ 
MEXICO 
10 MIGRO- METERS 
0 15 30 45 
0 10 20 30 40 50 60 
MIGROBARS 
120 WEST 10 100 90 80 
Fic. 7.—The distribution of LZ», the lunar semidiurnal air tide in barometric pressure, over North America, as shown by arrows, 
each of which specifies the annual mean LZ at the point at its centre. The lines diverging from the centres of the arrows are the 
forward halves of corresponding arrows specifying the mean ZL» for groups of four months, J (May to August), D (November to 
February), and # (March, April, September, October). 
D MONTHS 
AMPLITUDE 2, IN MM. 
90: 40° 30 20 10 ©O 10 
LATITUDE IN DEGREES 
20 30 S. 
(a) 
PHASE \> IN DEGREES, 
D MONTHS 
50 40 30 20 
LATITUDE IN DEGREES 
lo oO I) 20 30) & 
(b) 
Fig. 8—The dots indicate the latitude and the values of 
the amplitude /. (Fig. 8a, above) and phase ), (Fig. 8b, below) 
of the lunar semidiurnal air tide in barometric pressure in the 
mean of the D months (November to February), at various 
stations. The vertical lines indicate the probable range of 
uncertainty of the determinations. The curves are drawn 
through points giving the mean /» or d2 for groups of stations 
within narrow ranges of latitude. 
(N) INDICATES 
MEAN FROM N OBSERVATORIES 
AMPLITUDE £5 
Nine Ome 4 ORS Onc Onl) (e) lO ZOMTSONs: 
LATITUDE IN DEGREES 
(a) 
20 
A 40 
NW 
Sh MEO. 
WO rey 
os 80 4 Bee) 9) r 
x 
ac 
100 
120 
10 20 30 
Ni SON 40950)20) 110) 0 S. 
LATITUDE IN DEGREES (b) 
Fic. 9—Curves showing the average dependence on latitude 
of the amplitude I. (Fig. 9a, above) and phase » (Fig. 9, 
below) of the lunar semidiurnal air tide in barometric pressure, 
for the mean of the year and for groups of months J (May to 
August), D (November to February), and # (March, April, 
September, October). The curves are drawn through (or near 
to) points (X) each giving the mean [2 or dz for a group of sta- 
tions (the number of stations is indicated beside each point) 
within a moderate range of latitude. 
