Global Change Abstracts The Swiss Contribution - SCNAT

Global Change Abstracts – The Swiss Contribution | Atmosphere 47
The European summer of 2003 was characterised
by intense heat, prolonged isolation and suppressed
ventilation of the boundary layer which,
combined with large anthropogenic emissions
and strong fires, resulted in a build up of an unprecedentedly
high and long-lasting photochemical
smog over large parts of the continent. In this
work, a global chemistry and transport model
GEOS-Chern is compared with surface O-3 concentrations
observed in 2003 in order to examine
the extent to which the model is capable of reproducing
such an extreme event. The GEOS-Chem
reproduces the temporal variation of O-3 at the
Jungfraujoch mountain site, Switzerland, including
the enhanced concentrations associated with
the August 2003 heat wave (r = 0.84). The spatial
distribution of the enhanced surface O-3 over
Spain, France, Germany and Italy is also captured
to some extent (r = 0.63), although the largest concentrations
appear to be located over the Italian
Peninsula in the model rather than over Central
Europe as suggested by the surface O-3 observations.
In general, the observed differences between
the European averaged O-3 concentrations
in the summer of 2003 to those in 2004 are larger
in the observations than in the model, as the
model reproduces relatively well the enhanced
levels in 2003 but overestimates those observed in
2004. Preliminary contributions of various sources
to the O-3 surface concentrations over Europe
during the heat wave indicate that anthropogenic
emissions from Europe contribute the most to the
O-3 build up near the surface (40 to 50%, i.e. 30
ppb). The contribution from anthropogenic emissions
from the other major source regions of the
northern hemisphere, in particular North America,
tends to be smaller than those of other years.
The model indicates that the large fires that occurred
in that year contributed up to 5% (3 ppb) to
surface O-3 in close proximity to the fire regions
and less elsewhere in Europe. Biogenic volatile
organic compounds (VOCs) emitted by grass and
forest areas contributed up to 10% (5-6 ppb) of surface
O-3 over France, Germany and northern Italy,
which represents a contribution that is twice as
large than that found in 2004. These results in
terms of contributions from various sources, particularly
biogenic emissions, should be seen as
preliminary, as the response of vegetation to such
extreme events may not be well represented in
the model.
Environmental Chemistry, 2007, V4, N5, pp
285-292.
08.1-31
Velocity and temperature derivatives in high-
Reynolds-number turbulent flows in the atmospheric
surface layer. Part 1. Facilities, methods
and some general results
Gulitski G, Kholmyansky M, Kinzelbach W, Lüthi B,
Tsinober A, Yorish S
Israel, Switzerland
Meteorology & Atmospheric Sciences , Oceanography
, Geochemistry & Geophysics
This is a report on a field experiment in an atmospheric
surface layer at heights between 0.8 and
10m with the Taylor micro-scale Reynolds number
in the range Re-lambda = 1.6 - 6.6 x 10(3). Explicit
information is obtained on the full set of velocity
and temperature derivatives both spatial and
temporal, i.e. no use of Taylor hypothesis is made.
The report consists of three parts. Part I is devoted
to the description of facilities, methods and
some general results. Certain results are similar
to those reported before and give us confidence in
both old and new data, since this is the first repetition
of this kind of experiment at better data
quality. Other results were not obtained before,
the typical example being the so- called tear-drop
R - Q plot and several others. Part 2 concerns accelerations
and related matters. Part 3 is devoted to
issues concerning temperature, with the emphasis
on joint statistics of temperature and velocity
derivatives. The results obtained in this work are
similar to those obtained in experiments in laboratory
turbulent grid flow and in direct numerical
simulations of Navier- Stokes equations at much
smaller Reynolds numbers Re-lambda similar to
10(2), and this similarity is not only qualitative,
but to a large extent quantitative. This is true of
such basic processes as enstrophy and strain production,
geometrical statistics, the role of concentrated
vorticity and strain, reduction of nonlinearity
and non- local effects. The present experiments
went far beyond the previous ones in two main
respects. (i) All the data were obtained without
invoking the Taylor hypothesis, and therefore a
variety of results on fluid particle accelerations
became possible. (ii) Simultaneous measurements
of temperature and its gradients with the emphasis
on joint statistics of temperature and velocity
derivatives. These are reported in Parts 2 and 3.
Journal of Fluid Mechanics, 2007, V589, OCT 25,
pp 57-81.