Common volume satellite studies of polar mesospheric clouds with Odin/OSIRIS tomography and AIM/CIPS nadir imaging

• Published in: Atmospheric chemistry and physics 2019-10, Vol.19 (19), p.12455-12475
• Main Authors: Broman, Lina, Benze, Susanne, Gumbel, Jörg, Christensen, Ole Martin, Randall, Cora E.
• Format: Article
• Language: English
• Subjects: Aeronomy; Albedo; Atmospheric gravity waves; Bias; Brightness; Cloud albedo; Cloud properties; Clouds; Correlation coefficient; Correlation coefficients; Datasets; Dimensions; Function analysis; Gravitational waves; Gravity waves; Humidity; Imaging techniques; Instruments; Integration; Life cycle; Life cycles; Mesosphere; Moisture content; Particle size; Particle size distribution; Planetary waves; Polar mesospheric clouds; Properties; Properties (attributes); Questions; Resolution; Satellites; Scattering coefficient; Sensitivity; Size distribution; Spectroscopic analysis; Sublimation; Tides; Tomography; Water content
• ISSN: 1680-7324; 1680-7316; 1680-7324
• DOI: 10.5194/acp-19-12455-2019

Two important approaches for satellite studies of polar mesospheric clouds (PMCs) are nadir measurements adapting phase function analysis and limb measurements adapting spectroscopic analysis. Combining both approaches enables new studies of cloud structures and microphysical processes but is complicated by differences in scattering conditions, observation geometry and sensitivity. In this study, we compare common volume PMC observations from the nadir-viewing Cloud Imaging and Particle Size (CIPS) instrument on the Aeronomy of Ice in the Mesosphere (AIM) satellite and a special set of tomographic limb observations from the Optical Spectrograph and InfraRed Imager System (OSIRIS) on the Odin satellite performed over 18 d for the years 2010 and 2011 and the latitude range 78 to 80∘ N. While CIPS provides preeminent horizontal resolution, the OSIRIS tomographic analysis provides combined horizontal and vertical PMC information. This first direct comparison is an important step towards co-analysing CIPS and OSIRIS data, aiming at unprecedented insights into horizontal and vertical cloud processes. Important scientific questions on how the PMC life cycle is affected by changes in humidity and temperature due to atmospheric gravity waves, planetary waves and tides can be addressed by combining PMC observations in multiple dimensions. Two- and three-dimensional cloud structures simultaneously observed by CIPS and tomographic OSIRIS provide a useful tool for studies of cloud growth and sublimation. Moreover, the combined CIPS/tomographic OSIRIS dataset can be used for studies of even more fundamental character, such as the question of the assumption of the PMC particle size distribution. We perform the first thorough error characterization of OSIRIS tomographic cloud brightness and cloud ice water content (IWC). We establish a consistent method for comparing cloud properties from limb tomography and nadir observations, accounting for differences in scattering conditions, resolution and sensitivity. Based on an extensive common volume and a temporal coincidence criterion of only 5 min, our method enables a detailed comparison of PMC regions of varying brightness and IWC. However, since the dataset is limited to 18 d of observations this study does not include a comparison of cloud frequency. The cloud properties of the OSIRIS tomographic dataset are vertically resolved, while the cloud properties of the CIPS dataset is vertically integrated. To make these differen