Measurements of polar mesospheric clouds in infrared emission by MIPAS/ENVISAT

Abstract

We report on the infrared emission (10–13 μm) of polar mesospheric clouds (PMCs) as measured by Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) on board the Environmental Satellite (MIPAS/ENVISAT) during 19–21 July 2005 in the summer Northern Hemisphere. The spectral distribution of MIPAS radiances is well described by that simulated for ice particle emission at low temperatures and hence provides further evidence of the water ice nature of the PMC particles. The vertical profiles of integrated radiance clearly show an emission peak at tangent heights of 81–83 km, as expected from PMC emission. Ice particles' volume density retrieved from MIPAS spectra shows a layer of ice particles extending from 80.5 to 87 km and from about 60°N to the North Pole, well confined within the region where temperature is below approximately 150 K. The upper part of the ice particle layer then extends to altitudes higher than that observed by UV/visible measurements, which confirms the current understanding that PMCs cover the entire polar mesopause region. The altitude of the layer peak changes from 82.5–83 km at 70°N–90°N to slightly higher altitudes (83–85 km) at lower latitudes (60°N–70°N). MIPAS ice particle altitude/latitude distribution suggests that they are formed mainly close to the pole and then are transported upward and to lower latitudes by the ascending branch of the meridional circulation, confirming previous modeling.