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MIPAS discovers Antarctic nitric acid trihydrate (NAT) polar stratospheric cloud (PSC) belt

Michael Hoepfner(1), Niels Larsen(2), Reinhold Spang(3), Bei Ping Luo(4), Jun Ma(5), Synne Svendsen(2), Stephen Eckermann(6), Paola Massoli(7), Francesco Cairo(7), Marcel Snels(8), Guido Di Donfrancesco(9), Bjoern Knudsen(2), Uta Biermann(10), Gabriele Stiller(11), Thomas von Clarmann(1) and Herbert Fischer(1)

(1) Forschungszentrum Karlsruhe, Postfach 3640, 76021 Karlsruhe, Germany
(2) Danish Meteorological Institute, Lyngbyvej 100, 2100 Copenhagen, Denmark
(3) Forschungszentrum Jülich, Jülich, 52425 Jülich, Germany
(4) Institut für Atmosphäre und Klima, Schafmattstr. 30, 8093 Zürich, Switzerland
(5) Computational Physics, Inc., 8001 Braddock Road, Springfield, VA 22151, United States
(6) E. O. Hulburt Center for Space Research, 4555 Overlook Avenue SW, , Washington, DC 20375, United States
(7) Consiglio Nazionale delle Ricerche, Via Fosso del Cavaliere 100, 00133 Roma, Italy
(8) National Research Council , Via Fosso del Cavaliere 100 , 00133 Roma , Italy
(9) Ente per le Nuove tecnologie, l'Energie e l'Ambien, via Enrico Fermi, 45 , 00044 FRASCATI, Italy
(10) Referat für Umwelt- und Energiepolitik des SPD-Par, Wilhelmstraße 141, 10963 Berlin, Germany
(11) Forschungszentrum Karlsruhe, Postfach 3640, 76021 Karlsruheg, Germany

Abstract

The mid-infrared limb-emission sounder Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) on Envisat is the first instrument able to monitor continuously the development of PSC appearance and composition with full coverage of the polar regions even during polar night.

We have analyzed MIPAS wintertime observations over Antarctica with respect to PSC composition. Coincident lidar observations from McMurdo were used for comparison. By application of new refractive index data we could identify a distinct spectral signature at around 820 cm-1 observed by MIPAS as the nitrate nu_2-band of NAT. This has been the first evidence for the existence of NAT PSCs on a large scale. We could not find spectroscopic evidence for the presence of nitric acid dihydrate (NAD) from any MIPAS PSC observation.

During the initial phase of PSC development over Antarctica the MIPAS measurements reveal the formation of a belt of NAT PSCs in mid-June 2003. By mesoscale microphysical simulations we have shown that this sudden onset of NAT was caused by heterogeneous nucleation on ice in the cooling phases of large-amplitude stratospheric mountain waves over the Antarctic Peninsula and the Ellsworth Mountains. This suggests a more significant role for mountain waves in Antarctic PSC formation than has heretofore been appreciated. MIPAS observations of PSCs in a period of three weeks before this event show no indication for the presence of NAT clouds, but are consistent with supercooled droplets of ternary H2SO4/HNO3/H2O solution (STS). Simulations indicate that homogeneous surface nucleation rates have to be reduced by three orders of magnitude to comply with these observations.

 

Workshop presentation

Keywords: ESA European Space Agency - Agence spatiale europeenne, observation de la terre, earth observation, satellite remote sensing, teledetection, geophysique, altimetrie, radar, chimique atmospherique, geophysics, altimetry, radar, atmospheric chemistry