Change in turbopause altitude at 52 and 70° N
Permanent lenke
https://hdl.handle.net/10037/8585Dato
2016-02-26Type
Journal articleTidsskriftartikkel
Peer reviewed
Sammendrag
The turbopause is the demarcation between atmospheric
mixing by turbulence (below) and molecular diffusion
(above). When studying concentrations of trace species
in the atmosphere, and particularly long-term change, it may
be important to understand processes present, together with
their temporal evolution that may be responsible for redistribution
of atmospheric constituents. The general region of
transition between turbulent and molecular mixing coincides
with the base of the ionosphere, the lower region in which
molecular oxygen is dissociated, and, at high latitude in summer,
the coldest part of the whole atmosphere.
This study updates previous reports of turbopause altitude,
extending the time series by half a decade, and thus shedding
new light on the nature of change over solar-cycle timescales.
Assuming there is no trend in temperature, at 70◦ N there
is evidence for a summer trend of ∼ 1.6 km decade−1
, but
for winter and at 52◦ N there is no significant evidence for
change at all. If the temperature at 90 km is estimated using
meteor trail data, it is possible to estimate a cooling rate,
which, if applied to the turbopause altitude estimation, fails
to alter the trend significantly irrespective of season.
The observed increase in turbopause height supports a hypothesis
of corresponding negative trends in atomic oxygen
density, [O]. This supports independent studies of atomic
oxygen density, [O], using mid-latitude time series dating
from 1975, which show negative trends since 2002.