EGU General Assembly 2020
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the Creative Commons Attribution 4.0 License.

CALIOP PSC observations from 2006-2019

Michael Pitts1 and Lamont Poole2
Michael Pitts and Lamont Poole
  • 1NASA Langley Research Center, Science Directorate, Hampton, United States of America (
  • 2Science Systems and Applications, Inc., Hampton, United States of America

Even though the role of polar stratospheric clouds (PSCs) in stratospheric ozone depletion is well established, important questions remain unanswered that have limited our understanding of PSC processes and how to accurately represent them in global models.  This has called into question our prognostic capabilities for future ozone loss in a changing climate.  A more complete picture of PSC processes on polar vortex-wide scales has emerged from the CALIOP (Cloud-Aerosol Lidar with Orthogonal Polarization) instrument on the CALIPSO (Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations) satellite that has been observing PSCs at latitudes up to 82 degrees in both hemispheres since June 2006.  In this paper, we present a state-of-the-art climatology of PSC spatial and temporal distributions and particle composition constructed from the more than 14-year CALIOP spaceborne lidar dataset.  The climatology also includes estimates of particulate surface area density and volume density to facilitate comparisons with in situ data and measurements by other remote sensors, as well as with theoretical models relating PSCs to heterogeneous chemical processing and ozone loss. Finally, we compare the CALIOP PSC data record with the 1979-1989 SAM II (Stratospheric Aerosol Measurement II) solar occultation PSC record to investigate possible multi-decadal changes in PSC occurrence.

How to cite: Pitts, M. and Poole, L.: CALIOP PSC observations from 2006-2019, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3969,, 2020


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  • CC1: Comment on EGU2020-3969, Alexander James, 04 May 2020

    Thanks Michael et al. for your presentation.

    Could you comment on the shape of your NAT number density surves shown in the upper right?

    It looks like there are perhaps two of particles modes here?

    • AC1: Reply to CC1, Michael Pitts, 04 May 2020

      Hello Alexander- thank you for your interest, I'm sorry I couldn't be online for our session.  You are correct that NAT mixture distributions are bimodal.  We first observed this in the Pitts et al. (2013) paper where we examined PSC existence regimes by composition using a combination of CALIOP asnd MLS data.  We found that PSCs identified as NAT mixtures exhibit two distinct preferred modes of HNO3 uptake: a non-equilibrium mode that is closely aligned with the STS HNO3 uptake curve and a second mode that is more closely aligned with the NAT equilibrium HNO3 uptake curve. Trajectory analyses showed that NAT mixtures in the non-equilibrium mode have been below TNAT for only short periods of time. Since the growth of NAT particles is kinetically limited, the HNO3 uptake in these mixtures is dominated by the STS droplets. On the other hand, NAT mixtures in the second mode have been below TNAT for much longer periods of time allowing the thermodynamically favored NAT particles to approach equilibrium.   If you want to see more details on these analyses, please look at the Pitts et al. 2013 paper in ACP.