Measurements of noctilucent clouds in infrared emission by MIPAS/ENVISAT
Manuel López-Puertas(1), Bernd Funke(1), Maya García-Comas(1), Diego Bermejo-Pantaleón(1), Thomas von Clarmann(2), Udo Grabowski(2), Michael Höpfner(2), Gabriele Stiller(2) and Christian von Savigny(3)
(1) Instituto de Astrofísica de Andalucía (CSIC), Camino Bajo de Huétor, 50, 18008 Granada, Spain
(2) Forschungszentrum Karlsruhe, Universitat Karlsruhe, Hermann von Helmholtz Platz, 1, 76344 Eggenstein-Leopoldshafen, Germany
(3) University of Bremen, Otto Hahn Allee, 1, 28359 Bremen, Germany
Noctilucent clouds (NLCs), also called polar mesospheric clouds (PMCs), occur at the coldest regions of the atmosphere near the summer high latitude mesopause where they form a layer of a few kilometers wide, peaking near 83 km and located at latitudes poleward of 50 degrees. They are being discussed as potential early indicators of global change since they are very sensitive to temperature and water vapour concentration in that region. NLCs have been intensively studied by observations from ground, rockets (in situ), and space, as well as by sophisticated models. The observations of NLCs in emission in the infrared is, however, very difficult because of the low icy particle volume concentration and the very cold mesopause temperatures, thus requiring very sensitive instruments for their detection.
In this paper we report on the infrared emission (10-12 µm) of noctilucent clouds as measured by the MIPAS instrument on Envisat. We analyze the measurements taken by MIPAS in its NLC mode (39-102 km) during July 2005. The shape of MIPAS spectra in this region is very similar to that simulated for ice particle emission at low temperatures (below 150 K) and hence provide a further evidence of the water ice nature of the NLC particles. The simultaneous measurements of temperature from the MIPAS CO2 15 µm region allows us to retrieve the ice particles volume density. 3D (longitude, latitude, altitude) distributions of the ice particles volume density retrieved from MIPAS spectra for 19-21 July 2005 in the Northern Hemisphere are presented and analyzed from their comparison with previous measurements and model predictions.