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

Abstract

Abstract. We have analysed MIPAS (Michelson Interferometer for Passive Atmopheric Sounding) infrared measurements of PMCs for the summer seasons in the Northern (NH) and Southern (SH) hemispheres from 2005 to 2012. Measurements of PMCs using this technique are very useful because they are sensitive to the total ice volume and independent of particle size. For the first time, MIPAS has provided coverage of the PMC total ice volume from midlatitudes to the poles. MIPAS measurements indicate the existence of a continuous layer of mesospheric ice, extending from about ∼ 81 km up to about 88–89 km on average and from the poles to about 50–60° in each hemisphere, increasing in concentration with proximity to the poles. We have found that the ice concentration is larger in the Northern Hemisphere than in the Southern Hemisphere. The ratio between the ice water content (IWC) in both hemispheres is also latitude-dependent, varying from a NH ∕ SH ratio of 1.4 close to the poles to a factor of 2.1 around 60°. This also implies that PMCs extend to lower latitudes in the NH. A very clear feature of the MIPAS observations is that PMCs tend to be at higher altitudes with increasing distance from the polar region (in both hemispheres), particularly equatorwards of 70°, and that they are about 1 km higher in the SH than in the NH. The difference between the mean altitude of the PMC layer and the mesopause altitude increases towards the poles and is larger in the NH than in the SH. The PMC layers are denser and wider when the frost-point temperature occurs at lower altitudes. The layered water vapour structure caused by sequestration and sublimation of PMCs is present at latitudes northwards of 70° N and more pronounced towards the pole. Finally, MIPAS observations have also shown a clear impact of the migrating diurnal tide on the diurnal variation of the PMC volume ice density.

Understanding the Effects of Polar Mesospheric Clouds on the Environment of the Upper Mesosphere and Lower Thermosphere

“…First, the overall IWC values are lower in the SH. This reflects the well‐known pattern whereby PMCs are less abundant in the SH due to interhemispheric differences in middle atmospheric dynamics (Bailey et al, 2005; Garcia‐Comas et al, ; Hervig et al, 2013; Siskind et al, ). Second, there is greater scatter in the SH IWC values such that, even in midseason, there are numerous individual IWC points below 10 g/km 2 , while in the NH there is roughly a 50‐day period where SOFIE never sees IWC below 15 g/km 2 .…”

“…For both SOFIE and WACCM‐PMC, the NH IWC begins to increase in late May (Days 20–30), shows an apparent plateau in IWC during June, jumps up by about 20% around Day 55 (late June), and peaks around Day 85 (late July). The occurrence of peak IWC in late July partly reflects the fact that the latitudes of the SOFIE occultations are somewhat higher in late July (72°N) compared with solstice (66°N) and thus correspond to a region where IWC is normally greater (e.g., Garcia‐Comas et al, ) The magnitude of the peak (65–70 g/km 2 ) also agrees well between model and data.…”

“…Given that the IWC and H variations were in such good agreement with SOFIE and SABER, respectively, it is somewhat puzzling why the model overestimates the dehydration and underestimates the sublimation. We note that Michelson Inteferometer for Passive Atmospheric Sounding data (Garcia‐Comas et al, ) showed an H 2 O anomaly similar to SOFIE, or even less: about 0.5 ppmv depletion from 85–95 km and an enhancement of around 1.4 ppmv at 80 km (their Figure 10). Thus, the WACCM overestimate seems to be of some generality.…”

“…Data from the Michelson Inteferometer for Passive Atmospheric Sounding instrument also show much less dehydration than the 2–3 ppmv suggested by the model (cf. Garcia‐Comas et al, , their Figure 10). A model overestimate of dehydration has been seen in other simulations (e.g., Bardeen et al, ; von Zahn & Berger, ), so we conducted a study to investigate whether increased eddy diffusion would smear out the H 2 O profile and thus reduce both the dehydration and the sublimation.…”

Level 1b error budget for MIPAS on ENVISAT

“…MIPAS is a limb emission sounder measuring the atmospheric emission at tangent altitudes from about 6 to 70 km in nominal measurement mode. These measurements allow to 15 retrieve vertical and horizontal (along-track) distributions of temperature and more than 20 trace gases (e.g., Raspollini et al, 2015Raspollini et al, , 2013Wiegele et al, 2012;Funke et al, 2009;von Clarmann et al, 2009), including some isotopologues (e.g., Jonkheid et al, 2016;Steinwagner et al, 2007), aerosols (e.g., Günther et al, 2018;Griessbach et al, 2016) and clouds (e.g., Spang et al, 2018;García-Comas et al, 2016). Some species like bromine nitrate, ammonia or sulfur dioxide have been derived for the first time in the upper troposphere and stratosphere (Höpfner et al, , 2015.…”