This description
remains more or less the same when the threshold value is
10-fold increased to juwj ¼ 0:1m2 s2 (closed squares). Events
of this magnitude occur only on 17 July after 0915 EDT, the
diurnal variation being similar to the one described for the
lower threshold value albeit with lower values of D. Although
there are fluctuations in duration fraction of similar magnitude
during the afternoon, no synchronized fluctuations in
pollen concentration are observed. This may be caused by the
two-hourly pollen sampling periods during the afternoon that
act as a low-pass filter.