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Scientific Report 2007-2009<br />
Geophysics<br />
G4. Atmospheric optical remote sensing in Polar regions<br />
With climate problems becoming a critical issue, there<br />
is an increasing need for better monitoring the real<br />
changes affecting the atmosphere. In particular the Polar<br />
zones are known to be among the most sensitive to<br />
global changes.<br />
The Group of Atmospheric Physics runs a lidar<br />
system placed at Thule, Greenland, which is<br />
part of the international Network for the Detection<br />
of Atmospheric Composition Changes (NDACC)<br />
(http://www.ndsc.ncep.noaa.gov/). The network is<br />
composed of more than 70 high-quality, remote-sensing<br />
research stations for observing and understanding the<br />
physical and chemical state of the stratosphere and upper<br />
troposphere and for assessing the impact of stratosphere<br />
changes on the underlying troposphere and on<br />
global climate. The lidar (LIDAR, LIght Detection And<br />
Ranging), a radar-like instrument using a laser as radiation<br />
source and an optical telescope as receiver, is able<br />
to detect aerosol (by Mie scattering), minor constituents<br />
like water vapor (by Raman scattering), and temperature<br />
(by Rayleigh scattering) profiles from the ground<br />
up to the mesosphere (approximately 70 km).<br />
Figure 2: Atmospheric temperature profile at Thule measured<br />
by Rayleigh scattering lidar. Blue broken line: climatological<br />
temperature profile for January at latitude 75N.<br />
Red: radiosounding.<br />
Figure 1: Lidar system at Thule. The black case contains<br />
the 800mm telescope pointing vertically; the Nd:YAG laser<br />
(red case) is placed in the lower part of the structure.<br />
The lidar system was constructed at the University of<br />
Rome and installed in 1990 at Thule within a collaboration<br />
with the Danish Meteorological Institute (Figure<br />
1). The system uses several receiving channels, which<br />
can be used to obtain vertical profiles of backscatter<br />
cross-section and depolarization of atmospheric particulate<br />
at two wavelengths (λ = 532nm and λ = 355nm).<br />
The depolarization provides information on the physical<br />
phase (solid or liquid) of the aerosol. In the absence of<br />
aerosol and clouds, the lidar can provide temperature<br />
profiles up to the mesosphere by molecular Rayleigh<br />
scatter (Figure 2). In the last twenty years the system<br />
has had the possibility to gather a wide statistics by<br />
operating in very different atmospheric conditions,<br />
such as during the stratospheric aerosol enhancement<br />
after the Pinatubo eruption in 1991, during conditions<br />
of extremely low temperatures and during Sudden<br />
Stratospheric Warming conditions. Moreover due to the<br />
high variability of the Polar vortex, Thule often passes<br />
from within to without the vortex and vice-versa with<br />
large temperature changes allowing the monitoring of<br />
peculiar polar thermo-dynamical phenomena like the<br />
ozone laminae [1]. Narrow band interference filters permit<br />
the operation also in high background illumination<br />
although only for aerosol profiles. Both aerosol and<br />
temperature data are continuously <strong>download</strong>ed into the<br />
data base of NDACC. Presently the Thule station is run<br />
in collaboration with ENEA and INGV researchers who<br />
provide support and other complementary instrumentation.<br />
References<br />
1. G. Muscari et al., J. Geophys. Res., 112, D14304, (2007).<br />
Authors<br />
G. Fiocco, D. Fuà, M. Cacciani, A. di Sarra 8 , G. Muscari,<br />
T. Di Iorio, L. Di Liberto, F. Angelini, O. Lanciano, V.<br />
Ciardini, C. Tirelli, G. Casasanta, C. Di Biagio.<br />
http://g24ux.phys.uniroma1.it/<br />
<strong>Sapienza</strong> Università di Roma 169 Dipartimento di Fisica