166 AIR MASS ANALYSIS 
EXPLANATORY LEGENDS FoR FIGURES 4, 5, 6 AND 7 
FIGURES 4 AND 6 are charts constructed upon a surface of constant entropy 
(constant potential-temperature). For these cases the particular value of 
potential temperature chosen was 310°. Solid lines are lines of specific humidity 
while dotted lines are lines of elevation (in meters) of the chosen surface above 
sea level. “M’” signifies the center of a moist tongue, ‘“D” the center of a dry 
tongue. “H” and “L” are entered at the crests and troughs of the isentropic 
sheet. The numbers to the right of the aerological stations are, in the order 
listed, the specific humidity, the elevation, and the relative humidity at the given 
isentropic sheet. To the left of the station is entered the pressure, in millibars, 
of the layer bounded by the 305° and 310° surfaces of potential temperature. 
The change from day to day in these values offers indications of convergence 
and divergence. Winds at the isentropic surface are shown by arrows, the 
number of half-barbs being roughly equivalent to Beaufort numbers of the 
scale of wind force. Clouds are indicated by the international cloud symbols. 
Subseripts give the amount of cloud and arrows the direction of movement. 
If the letter ‘“‘b” appears following the symbol the clouds are below the isentropic 
sheet, if elevations are given the clouds penetrate the sheet, and if nothing is 
appended they are above it. An asterisk (*) indicates that the clouds are 
within the range of the sounding, yet no height was recorded. Heavy arrows 
represent the probable path of the tongues with respect to the isentropic surface 
(that is, choosing a codrdinate system fixed to the isentropic surface). 
FIGURES 5 AND 7 are vertical cross-sections extending north-south from 
Sault Ste. Marie, Michigan, to Pensacola, Florida. The evenly spaced hori- 
zontal lines represent full kilometers of height. Solid lines are drawn for 
specific humidity, dashed lines for potential temperature. The humidities in 
the individual soundings are entered to the left and the potential temperatures 
to the right of the vertical. Winds are drawn so that north is to the left 
of the cross-section. For example, at 3 km over Dayton on the 28rd (fig. 5) 
there is a N wind of force six. Clouds are indicated, as in figures 4 and 6, by 
the international system; those above the soundings are either above the top 
of the ascent, or, if accompanied by an asterisk, within the levels penetrated 
by ne sounding but not placed specifically. Here again ‘“M” stands for moist, 
“D” for ry. 
