and aerosols stratospheric profiles by a DIAL lidar. The particular results of 1991 in relation with the volcanic events of Mount. Pinatubo and. Mount. Hudson, and.
N95- 11036
SYSTEMATIC
STRATOSPHERIC
S. Godin,
OBSERVATIONS ON THE AT DUMONT D'URVILLE
A. Sarkissian,
C. David,
G. M_gie, J.P. Pornmereau,
P. Aimedieu, J. Piquard, E. Le Bouar d'Arronomie du CNRS, Verrirres le Buisson,
Service
L. Stefanutti,
M. Morandi,
CNR,
Florence,
ABSTRACT
by
a
SAOZ
Cloud
UV-Visible
observations
spectrometer,
by a hackscatter
F. GoutaU, France
M. del Guasta
with special
attention
given
and
2.
SAOZ
OBSERVATIONS
A zenith sky looking broad resolu'tion (1 nm) UV-Visible
position discussed.
continuously
since
in real time.
The
1.
the
polar
vortex
over
Dumont
d'Urville
d'Analyse par Observations d'Arronomie, was installed
are
Continuous observation Antarctica is performed
operated
of NO2, 03, aerosols instrument UV-Visible
continuously
contents as well stratospheric clouds. Ozone
Lidar
Florence, aerosols
of the polar stratosphere over since 1988 at the french base of
day at twilight
since
1988
and stratospheric spectrometre provides
in cooperation
lidar measurements and polar stratospheric
The
lidar
and temporal term evolution soundings the
ozone
launched
instrument
presence of project (Polar
with
the IROE
of
of the vertical profile of clouds are performed since
are also performed daily
for
temperature by the various experiments covering
provides
continuity, allowing of the stratosphere.
destruction
the first
years
vertical
an increased
Parallely,
measurement
french over
four
high
recorded
spectra
are transmitted
are processed
by the satellite
data
rate
local
wind
Met. Office. an extended
of
Results period
of of
of operation
will
the same
way from
and
nm.
470
87 ° and 91 ° SZA and retrieved
its numerous
In addition,
The
four
ones
of
and half 1992
the
narrow color
years of results
up to mid-May,
after
bands of
the
between zenith
410 sky
is
including
the preliminary
are displayed
on figure
1. In
average, during the period, ozone and more and more minima can
decreases progressively be observed during the
spring when the vortex approaches a marked seasonal variation with
the station. NO2 displays a maximum in summer
(CI) also shows
during
radiosondes
between
during the polar day and a minimum in winter during the polar night, when the diurnal variation vanishes. The color of the zenith sky at twilight, expressed in term of color index
resolution
thus to study the short Since 1991, ECC ozone
with
period. the
The
designed in Service 1988 and operated
investigated by calculating for each spectrum a color index, defined as the ratio between the fluxes observed at 550 and 350 nm.
NO2 and 03 total
as indications on the In the frame of the POLE
Experiment)
clouds : which is
1989 (Stefanutti et al.), with the addition since January 1991 of the ozone vertical distribution in the [5-40 km] altitude range.
Z_nithales) in January
and high (Systbme
carefully removing interfering absorptions of Oa at 477 and 576 nm, and H20 at 505 and 590 nm. NO2 is calculated in
d'Urville (66°S, 140°E). This programme, by the TAAF (terres Australes et Antlactiques includes several instruments for the
measurements The SAOZ
then. results
band (300-600 nm) spectrometer SAOZ
collection system ARGOS for first evaluation and reanalysed later after reception of the data containing diskettes. Ozone is measured in the visible Chappuis bands (450-540 nm) twice a
INTRODUCTION
Dumont developped fran_aises),
periods
Polar lidar
more recently, vertical ozone profiles by ECC sondes and ozone and aerosols stratospheric profiles by a DIAL lidar. The particular results of 1991 in relation with the volcanic events of Mount Pinatubo and Mount Hudson, and the of
to the winter-spring
characterized by the appearance of stratospheric clouds and depleted ozone contents. The observation above Dumont d'Urville of the volcanic events which occurred in 1991 Mount Pinatubo and Mount Hudson - will also be discussed.
Results of different routine measurements performed in Dumont d'Urville (66°S, 140°E) since 1988 are presented. They include the seasonal variation of total ozone and NO2 as Stratospheric
CONTINENT
Italy
here,
measured
ANTARCTIC
automn
are
and
a systematic
early
winter,
which can be explained
and
seasonal drifting
variation towards
by the progressive
(redder the
blue
downward
ira Iate later) shift of
the altitude of the minimum temperature and therefore of PSC formation. Larger blueings are observed in 1991 since
these time
August, volcanic
be presented 561
which are interpreted by the arrival of low altitude aerosols likely released by the Mount Hudson
500 dso
3.
OZONE
POLAR OZONE LIDAR EXPERIMENT
Polar
35o
stratospheric
clouds
observations
3oo 40o 250 2oo
The
_
first step of the POLE
Italian research
-
elastic backscatter and stratospheric a1.,1989) pulse
0 -
--
Mormng
--
tvlntng
experiment,
French cooperation was the implementation
organized
programme at Dumont
operated
at 532 nm with
and a repetition
a linearly
Color
TEMPERATURE
(50
-.
of
three
laser parallel
differential aerosols and
types
of
lidar polar
rate (10HZ), and km altitude range
scattering
layers
are
observed on the lidar data in the range 8 - 35 km : background aerosols, cirrus clouds at lower altitudes and
hPe)
polar stratospheric the whole altitude
-4O
_,
signature
on both
planes relative to the emitted In January 1991, this system
was replaced by a multiwavelength instrument meant to measure both the
Index
polarized
rate of 4 HZ. Signals
and perpendicular polarization laser radiation were collected.
The 24e
an
lidar designed for both tropospheric clouds clouds measurements. The system (Sacco et
stratospheric clouds with a higher repetition the ozone vertical distribution in the 5-40 (Stefanutti et al., 1991). !_i^
under
for Antarctic d'Urville of an
when starts
-so
clouds which are expected range above the tropopause
to form over during winter,
the temperature drops below 195°K. Detection of PSC around mid-June and ends around mid-September,
-6o
although
most
of them
are
seen
in July
and
August.
The
-70
interannual dependance the local meteorological
-8o -9o 200
400
600
BOO
1000
'200
_400
the presence of low tropospheric detection of clouds located at higher
_600
only Figure
1 : Four years of 5 days running means of total ozone, nitrogen dioxide and color index at twilight observed
by the SAOZ
UV-Visible
a few measurements
to the
bad weather
month.
The
scattering of the is
made
radiosondes ballons time. Nervertheless, distinguish
another
in Chile. aerosol
reddening
of
Later,
cloud the
color
strongly correlated and therefore with indicate
artefact Although affected
the
to reach
index.
The
15th
of
large
CI
causing
is located
outside
a
fluctuations
the vortex
vortex ozone,
to the
located by
this
upward at
drift
higher
effect,
of
the
altitudes
and never
NO2
is
scattering
and
dramatically
13 and 25
ratio type of
varying from PSC measured
2 to 6. with the
difficult
by
clouds
above
range
2i. Both PSC show
(figure
The
little
mare
event
measurements
reduced
is
of the
not during
the
heterogeneous
destruction
which
operates
during
daylight
period.
the permanent
of
the night
N205 only
a cirrus
1991
onto
20th
according
and
unfortunately 562
ot
Jt'lly to
during the
stopped
with
eruption
the
of
by
respectively,
the
particles,
bursting
of
the
18 km during winter ratio values allow to
altitude
Philippines in June 1991. aerosols events were detected
result
formed
the
25 km
compared to the previous years and does not increase before the arrival of the permanent daylight. This is believed to be aerosols
this
between
spherical
or
non
cloud
located
a scattering
at 9 km ratio
of
relatively high value of the scattering ratio for the former cloud may indicate the presence of a type II PSC according to the classific:_tion of Toon (Toon et al., 1990).
layer.
therefore
observed
during
3 but the higher one is ch_u'acterized by a depolarization ratio of 25 _7_as compared to less than 5 % for the lower one. The
inside. The measured total ozone decrease with the reddening of the color index is due to an due
1991, due
prevailed
spherical particles. This is illustrated by the case of August 3_ 1989 where two PSC clouds were detected at 20 km and
September,
the station,
with the movements of the polar the 50hPa temperature and total
that this cloud
penetrates associated
around
appears
in August
which
generally above the depolarization
betv, een
on for
clouds precludes the altitudes. In particular,
were possible
conditions
PSC are generally
km with a Differentiation
spectrometer.
temperature
eruption
of PSC sighting depends highly conditions at Dumont d'Urville
of
respect mount
to
Pinatubo
Some unusually very on the 532 nm channel a
period
radiosonde at 18 km on
of
cold day.
in
the
strong around
temperature,
measurement that
aerosols
The
which absolute
ZE-O?
DUMONT
3O
i
D'URVILLE
I
p
1991/09/04
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i
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i
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