the downwind (NW) field was 26 V/m. Mean changes in the upwind
fields were much less than these values (Table V).
C. Ion Concentrations
Cumulative distributions for the measurements of ion concentrations
by station and by wind condition are given in Fig. 6
and 7 for positive and negative polarities, respectively. As expected
there were many similarities with the distributions for
electric-field measurements in Fig. 3. The downwind ion distributions
tend to diverge from the upwind and no-wind distributions
at about the 70th percentile for positive ions and above
the 90th percentile for negative ions. Over most of the distributions
the upwind positive ion concentration had lower values
than during the other wind conditions. At the NW station the
no-wind distribution showed enhancement above the upwind
case, but at other sites it did not.
Fig. 5 includes upwind and downwind ion concentrations at
ground level for both polarities during periods of sustained wind
in either direction. There was no difference between the levels
of upwind and downwind negative ions during these periods.
However, there were elevations in the downwind positive ion