Operation and Results of ‘Project Pluvius’ 
Tor BERGERON 
Royal University of Uppsala, Uppsala, Sweden 
PI PI 
The results of all my work on orographic and 
other precipitation distributions showed that 
the official network in no country was dense 
enough. So I had to construct an ‘instrument,’ 
which, of course, is not a laboratory instrument 
in the ordinary sense; but after all 1t 1s compara- 
ble to an instrument, because it is exceedingly 
complicated, consisting, during the summers of 
1955 and 1956, of not less than a thousand rain 
gages of the type shown in Figure 1. Thus we 
had to use very cheap ones; in fact, the present 
cost is only one dollar for this ‘automatic rain 
gage Pluvius.’ We used it to build our rather 
complicated measuring ‘instrument’ in order to 
find out something more about the real distribu- 
tion of precipitation. I am accustomed to having 
a lot of questions concerning this instrument and 
how it works, and about its possible errors. I 
am prepared to answer them in the discussion. 
As to regions to select for our ‘instrument’-— 
that is, for this special network of gages—when 
starting our project during the autumn of 1953, 
we thought that one ought to test the whole set 
up in three different respects. (1) How the in- 
strument would work in the field. (2) If it were 
possible to get enough observers evenly distribu- 
ted and working without pay. (3) We also wanted 
to get some knowledge as to the interior structure 
of different kinds of rain mechanisms, for in- 
stance, the warm-front rain and the cold-front 
rain, when not disturbed by orography. So we 
selected an area 20 by 20 miles around Uppsala 
that was easy to reach, and which, I thought, was 
so flat that there would be no appreciable oro- 
graphic effects. The measurements went on for six 
weeks (in October and the first part of Novem- 
ber). Unfortunately, we had only a few big rains, 
but it turned out that they were very suitable 
after all. On October 14-16, a front lay across 
southern Sweden with a stationary rain area and 
northeasterly winds on its northern side. Figure 
2 shows the results of the measurements during 
the first 12 hr of this period. Notice that it is the 
night and not the day period, so there would be 
very little convection. When we first got the 
figures, I thought they did not show much, but 
when plotted on an appropriate map showing 
the regions with forest (green on the original base 
map), and those without, a most surprising con- 
nection appeared between the shaded areas and 
much precipitation, and the white areas and a 
minimum of it. See Figures 2 and 3 where wood- 
land is indicated by the legend. 
Now, I must spend one minute on other proj- 
ects of a similar kind. You might, for instance, 
Fia. 
1—The automatic rain gage Pluvius, with 
a cork-float lifting the measuring rod; ratio col- 
lecting area to cylinder area = 5; cost $1 
OZ 
