. ATMOSPHERIC PRESSURE 4 3 
» DISCUSSION 
Departures from 
Normal Regional Values of Pressure 
The mean daily values of atmospheric pressure as 
determined on the cruise of the Carnegie can be expect- 
ed to have little climatological significance, inasmuch 
as the time spent in any region with more or less homo- 
geneous climate was short. Therefore, we are hardly 
justified in assuming such day-to-day observations 
made on board a rapidly moving vessel to be truly repre- 
sentative of pressures within a fixed region, no matter 
how large this region may be. It has been possible, how- 
ever, to determine the departure of Carnegie pressures 
from monthly normals which have been computed from 
pressure data previously accumulated over the North 
Atlantic Ocean and the North and South Pacific oceans. 
Continuous observation of air pressure was obtained 
for a period of 344 days during the cruise. The correct- 
ed hourly values of barometric pressure arranged 
chronologically are presented in appendix III (table 77); 
the position of the vessel at local noon is entered at the 
left of the table. From these values it has been possible 
to determine departures of pressure from predetermined 
values of normal pressure for the various regions, by 
months, as given by Bartholomew's Physical Atlas, 
British Admiralty charts, Pilot Charts of the U.S. . 
Hydrographic Office, Hoffmeyer charts, publications of 
the Japanese Imperial Marine Observatory, and the 
Deutsche Seewarte charts. These sources usually gave 
very nearly the same normal values for the various re- 
gions, but where there was disagreement the most re- 
cent, and presumably most accurate, source was chosen. 
The normal values of atmospheric pressure for the At- 
lantic Ocean have been determined from the monthly 
means of many more observations than have the monthly 
Le 
normals for the Pacific Ocean. The Atlantic normals, 
therefore, should more nearly approach the true nor- 
mals for the region. 
Table 2 contains data concerning the differences be- 
tween the Carnegie mean pressures and the normal 
mean pressures for the twenty-two groups outlined in 
table 1. From these data the following general conclu- 
sions may be drawn: 
1. Pressures were slightly above normal during the 
first part of the cruise from Hamburg to Iceland, and 
until the Gulf Stream was crossed. 
2. Pressures were slightly below normal for the 
part of the cruise between the Gulf Stream and Barbados. 
3. Pressures averaged about normal over the Carib- 
bean Sea and the South Pacific Ocean until the South Pa- 
cific High-Pressure Belt was reached, although for eight 
days during December 1928, when the vessel was very 
nearly in the center of the South Pacific High-Pressure 
System, the barometer averaged 5 mm higher than the 
normal for that region. 
4. Throughout the western part of the cruise in the 
Pacific, which lay largely in the equatorial and trade- 
wind belts, the observed pressures were near normal 
for those belts. 
5. During June and July 1929, between latitudes 35° 
and 52° north and longitudes 141° east and 150° west, 
the mean values of atmospheric pressure averaged from 
2 to 6 mm higher than the ten-year mean for this region 
as given by the tables of the Japanese Marine Observa- 
tory [see 1 of section of references, p. 61]. This condi- 
tion indicated a greater northwesterly extension of the 
North Pacific High-Pressure Belt during these months. 
6. Pressures on the outward cruise from San Fran- 
cisco to Apia averaged slightly below normal, which 
would indicate that the condition mentioned in the previ- 
ous paragraph continued throughout this period. 
Table 2. Comparison of Carnegie and normal values of atmospheric pressure for groups, 
Carnegie, 1928-29 
Differ - 
No. [Mean | Carnegie 
o °o mm wien 

if July-Aug. 9 56.3 N 
II August 4 42.8N 
il August 13 29.0 N 
IV -—s— Aug.-Sep. 21 11.8N 
Vv October 9 13.8 N 
VI Oct.-Nov. 12 4.0N 
VII 
8 Nov.-Dec. 35 16.5 S 
b February tf 13.1S 
VI December 8 37.28 
Ix January 14 24.78 
x February 12 12.38 
XI March 21 16.88 
XII April-May 32 9.7N 
XU 
a) June 13 34.3 N 
b July 3 39.6 N 
XIV July 19 47.7N 
XV July 7 41.5 N 
XVI September 5 34.1 N 
XVII 
a September 8 27.8 N 
b Sep.-Oct. 8 27.0 N 
c October 14 25.2 N 
XVIII Oct.-Nov. 20 0.18 
mm 
40.7 W 762 759 +3 
47.8 W 766 764 +2 
42.0 W 763 765 -2 
43.0 W 760 762 -2 
71.0 W 759 759 0 
81.0 W 758 759 -1 
104.3 W 763 762 +1 
119.4 W 759 759 0 
96.7 W 770 765 +5 
83.3 W 763 763 0 
88.2 W 760 760 0 
147.9 W 759 759 0 
168.7 E 759 759 0 
143.1 E 760 758 +2 
149.4 E 765 759 +6 
179.5 W 763 760 +3 
131.8 W 764 764 0 
126.3 W 761 763 -2 
136.6 W 762 764 -2 
155.1 W 765 765 0 
140.7 W 760 763 -2 
150.5 W 757 758 -1 

