6 METEOROLOGICAL RESULTS OF LAST CRUISE OF CARNEGIE 
Table 6. Unperiodic amplitudes of atmospheric pressure classified according to number 
of days and latitude range, Carnegie, 1928-29 








Unperiodic Latitude range 
daily 25°N- 5°S- Se 
mm_— ‘ 
0- 2 7 17 28 27 29 28 11 31 29 20 7 
2- 4 3 13 5 5 3 16 18 14 4 2 2 
4- 6 6 5 2 3 onc sec Soc oa acc aK és 
6- 8 1 3 1 “08 
8-10 ae 1 2 5 
10-12 = 1 aoe or 
Total 17 40 35 38 32 44 29 45 33 22 9 

Table 7. Unperiodic daily amplitude of pressure, 
Gauss, 1901-03 
Latitude Amplitude | Latitude Amplitude 
= mm = mm 
50N 0.73 0 1.99 
40N 0.83 10S 2.01 
30 N 1.08 20S 1.50 
20 N 1.74 30S itl 
10 N 1.86 40S 0.94 
The periodic daily amplitude of pressure measured 
by the difference between the highest and lowest mean 
hourly values is, as shown in table 5, clearly dependent 
on latitude. This fact may be emphasized by comparing 
the values given in the bottom line of table 5 with the 
values of the periodic daily amplitude observed on the 
Gauss [2] in the Atlantic Ocean. The only exception to 
this decrease in amplitude with increase in latitude oc- 
curred within the range of latitude 45° to 55° north, in 
which the small diurnal range of 0.37 mm was recorded. 
This unusually small value, which will appear conspicu- 
ously in the amplitude of the 12-hour pressure wave, is 
probably related directly to the small diurnal range of 
temperature in these latitudes. 
Diurnal Pressure Oscillations * 
General Discussion 
Table 5 gives the hourly values of the diurnal ine- 
qualities of pressure for the various latitude ranges. 
For each range in latitude the departures have been sub- 
jected to Fourier analysis and the result has been ex- 
pressed in one of the following forms: 
(aycos t+ b;sin t) + (agcos2t + bo sin2t) + 
(ag cos 3t - bg sin 3t) + (aq cos 4t + basin 4t) = 
cysin (t+ $4) + C9Sin (2t + $9) + 
c3 sin (3t + $3) + cgsin (4t + $4) (1) 
where a and b are the Fourier coefficients, c the ampli- 
tude of the oscillation, t the time from local midnight 
expressed in degrees, and ¢ the time, also expressed in 
degrees, which fixes the phase of the oscillation in local 
time. The Fourier quantities so obtained for the vari- 

2 Much of the material in this section has appeared 
in Beitr. Geophysik, vol. 39, pp. 337-355 (1933). 
ous ranges of latitude represent the amplitudes and 
phase angles of the pressure waves (table 8). 
The 24-hour Period 
The 24-hour wave, represented by cj and ¢j in 
(1), appears to be chiefly dependent on temperature. 
Therefore, as would be expected, the amplitudes and 
phase angles as computed from the Carnegie data are 
very irregular, because of changes in season, variation 
in meteorological conditions, and differences in location 
with respect to land and water bodies. With regard to 
the amplitudes it is sufficient to state that the Carnegie 
data show that such values are greatest near the equator 
(0.453 mm), and decrease toward the poles as the peri- 
odic waves become masked by the pressure waves ac- 
companying cyclonic and frontal movements. The phase 
angles are fairly regular throughout the ranges of lati- 
tude between 15° north and 25° south, the maximum 
pressure occurring between 05h 32m and 06h 24m (7° to 
354°), local mean time. From similar pressure obser- 
vations over the ocean, Hann [3] and Meinardus [4] found 
that the phase angle (#1) crossed into the third quadrant 
(180° to 270°) at about latitude 30° north. According to 
the Carnegie data, however, this transition appears to 
occur between latitudes 35° and 45° north (table 8). 
The 12-hour Period 
The 12-hour pressure oscillation appears to have 
been given more attention by investigators than have the 
24-, 8-, and 6-hour periods. Because this wave is less 
dependent on local temperatures than the 24-hour wave, 
it tends toward greater regularity with regard both to 
amplitude and to phase angle. Simpson [5] has shown 
that this double diurnal oscillation of the barometer can 
be regarded as consisting of two vibrations: one the re- 
sult of waves traveling around the earth from east to 
west, and the other of an oscillation between the poles 
and equator. According to Simpson [5], the first (paral- 
lel to the circles of latitude) may be represented by the 
expression 
C2 = 0.937 cos3@ sin (2x - 154°) (2) 
and the other (parallel to the meridians) by 
C’g = 0.137 (sin@@ - 1/3) sin (2x-105°-2a) (3) 
A small seasonal variation exists, with maxima at 
the equinoxes and minima at the solstices [5, 6, 7]. 
