The diurnal variation of D during 16 July at the lowest threshold
value juwj>0:01m2 s2, presented in Fig. 14a, shows amore or
less constant value of about D 0.3 between 0700 and 1900
EDT. At first, fluctuations in the duration fraction do not seem
to be related to variations in pollen concentration. However,
when the threshold value is increased to juwj>0:4m2 s2
(closed symbols, ‘‘extreme’’ events with reduced values of D),
fluctuations become much larger. It can now be clearly
discerned that during the sampling period 0900–1000 EDT,
just before the pollen concentration reaches a minimum, the
‘‘extreme’’ event duration fraction peaks (D = 0.13 at 0930 EDT)
and then decreases to aminimum (D = 0.06 at 1000 EDT) during
the same sampling period that pollen concentrations are
minimal. Subsequently, the duration fraction rises sharply
again to a value of D = 0.13 at 1015 EDT.
The diurnal variation of D during 16 July at the lowest threshold
value juwj>0:01m2 s2, presented in Fig. 14a, shows amore or
less constant value of about D 0.3 between 0700 and 1900
EDT. At first, fluctuations in the duration fraction do not seem
to be related to variations in pollen concentration. However,
when the threshold value is increased to juwj>0:4m2 s2
(closed symbols, ‘‘extreme’’ events with reduced values of D),
fluctuations become much larger. It can now be clearly
discerned that during the sampling period 0900–1000 EDT,
just before the pollen concentration reaches a minimum, the
‘‘extreme’’ event duration fraction peaks (D = 0.13 at 0930 EDT)
and then decreases to aminimum (D = 0.06 at 1000 EDT) during
the same sampling period that pollen concentrations are
minimal. Subsequently, the duration fraction rises sharply
again to a value of D = 0.13 at 1015 EDT.
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