| Meteors are an important source for (a) the metal atoms of the
upper atmosphere metal layers and (b) for condensation nuclei, the
existence of which are a prerequisite for the formation of
noctilucent cloud particles in the polar mesopause region. For a
better understanding of these phenomena, it would be helpful to
know accurately the annual and diurnal variations of meteor rates.
So far, these rates have been little studied at polar latitudes.
Therefore we have used the 33 MHz meteor radar of the ALOMAR
observatory at 69° N to measure the meteor rates at this location
for two full annual cycles. This site, being within 3° of the
Arctic circle, offers in addition an interesting capability: The
axis of its antenna field points (almost) towards the North
ecliptic pole once each day of the year. In this particular
viewing direction, the radar monitors the meteoroid influx from
(almost) the entire ecliptic Northern hemisphere.
We report on the observed diurnal variations (averaged over one
month) of meteor rates and their significant alterations
throughout the year. The ratio of maximum over minimum meteor
rates throughout one diurnal cycle is in January and February
about 5, from April through December 2.3±0.3. If compared
with similar measurements at mid-latitudes, our expectation, that
the amplitude of the diurnal variation is to decrease towards the
North pole, is not really borne out.
Observations with the antenna axis pointing towards the North
ecliptic pole showed that the rate of deposition of meteoric dust
is substantially larger during the Arctic NLC season than the
annual mean deposition rate. The daylight meteor showers of the
Arietids, Zeta Perseids, and Beta Taurids supposedly contribute
considerably to the June maximum of meteor rates. We note, though,
that with the radar antenna pointing as described above, all three
meteor radiants are close to the local horizon but all three
radiants were detected. |