Polar mesospheric clouds: Infrared measurements from the Midcourse Space Experiment

Abstract

[1] Spatial Infrared Imaging Telescope (SPIRIT) III radiometer on the Midcourse Space Experiment (MSX) satellite measured highly structured infrared, IR, emission from polar mesospheric cloud (PMC) ice particles at northern latitudes above 51 degrees on 22 July 1996 in the 11.1 to 13.2 and 18.2 to 25.1 mm radiometer channels, bands C and E, respectively. Measurements of the PMC thermal emissions included the observation of an extended cloud at 84.8°N and 325.6°E at 0313:25 UT, a local solar time of approximately 0056. In this Earth limb observation, the radiance due to the PMC has been isolated from other sources-atmospheric emission, nonrejected off axis radiation from the terrestrial surface and zodiacal radiance-and inverted to determine the volume emission rates of the ice particles at a spatial resolution of 0.3 km in the altitude range from 83.4 to 86.4 km. The band C PMC volume emission rate profile has a maximum value at 84.0 ± 0.3 km and decreases to one half the peak value at 85.0 and 83.5 km. Temperatures in the range from 143 ± 7 to 130 ± 8 K and ice volume densities from 1.5 to 0.5 Â 10 À13 cm 3 per cm 3 were determined from the LWIR volume emission rates at altitudes from 83.4 to 86.4 km. The PMC ice densities are equivalent to an enriched gas phase water mixing ratio of 8 to 16 parts per million by volume, ppmv, and a vertical column mass density of 3.3 Â 10 À8 gms cm À2 in this observation.

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

“…The spectral distribution of radiances measured by MIPAS in the 770–930 cm −1 region is very similar to that simulated for ice particle emission at low temperatures (below 150 K). This provides further evidence (after that of Hervig et al [2001], Eremenko et al [2005], Grossmann et al [2006] and O'Neil et al [2008]) of the water ice nature of the PMC particles. As a further check, the regions where MIPAS detected PMCs were compared to those derived from SCIAMACHY data and it was found that they coincide very well, although the percentage of scans with PMCs in the 60°N–90°N region is larger in SCIAMACHY than in MIPAS, probably because of the better sensitivity of SCIAMACHY (measuring in the UV) compared to MIPAS (observing in the infrared).…”

“…The spectral shape of the simulated signal closely resembles the MIPAS coadded spectrally degraded PMC spectra (Figure 2). This provides further evidence (after that of Hervig et al [2001], Eremenko et al [2005], Grossmann et al [2006] and O'Neil et al [2008]) of the water ice nature of the PMC particles.…”

“…[6] While PMCs emit thermal radiation, their observation by infrared emission techniques is very difficult because of the low icy particle volume density and the very cold mesopause temperatures, thus requiring very sensitive instruments for their detection. Actually, only two observations in the infrared, in emission, have been so far reported: that taken by CRISTA [Grossmann et al, 2006] and by the SPIRIT [O'Neil et al, 2008] instruments. Infrared emission spectroscopy, however, has the advantage that it can also measure PMCs under dark conditions and hence might provide a better knowledge of their spatial distribution.…”

Measurements of global distributions of polar mesospheric clouds during 2005–2012 by MIPAS/Envisat

“…While the lidar signal varies with r 6 , the MIPAS (in IR emission) and SOFIE (in IR extinction) signals change with the total ice volume density. As the ice particle size decreases towards higher altitudes (Baumgarten and Fiedler, 2008;Hervig et al, 2009b;Pérot et al, 2010), MIPAS and SOFIE are then more sensitive than lidars to clouds at higher altitudes. The highest altitude of PMCs derived from MIPAS NLC mode measurements is largely variable, as can be seen in the typical examples shown in Fig.…”

“…(e.g. Baumgarten and Fiedler, 2008;Fiedler et al, 2009;Gumbel and Witt, 1998;Bailey et al, 2005;DeLand et al, 2003;Petelina et al, 2006;von Savigny et al, 2005von Savigny et al, , 2007von Savigny and Burrows, 2007;Pérot et al, 2010;Russell III et al, 2009); as well as sophisticated models (e.g. Berger and Zahn, 2002;Berger and von Zahn, 2007).…”