EGU2020-2850
https://doi.org/10.5194/egusphere-egu2020-2850
EGU General Assembly 2020
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Microphysics of Antarctic precipitation in climate models : recent advances and challenges

Étienne Vignon1, Josué Gehring1, Simon P. Alexander2, Georgia Sotiropoulou3, Nikola Besic4, Nicolas Jullien1, Noémie Planat1, Jean-Baptiste Madeleine5, and Franziska Gerber6,7
Étienne Vignon et al.
  • 1École Polytechnique Fédérale de Lausanne, Laboratoire de Télédetection Environnementale, Lausanne, Switzerland (etienne.vignon@epfl.ch)
  • 2Australian Antarctic Division, Hobart, Tasmania, Australia
  • 3Laboratory of Atmospheric Processes and their Impacts (LAPI), École Polytechnique Fédérale de Lausanne, Switzerland
  • 4Météo France, Toulouse, France
  • 5Laboratoire de Météorologie Dynamique / Sorbonne Université, Paris, France
  • 6CRYOS, École Polytechnique Fédérale de Lausanne, Switzerland
  • 7WSL Institute for Snow and Avalanche Research SLF, Davos, Switzerland

The current assessment of the Antarctic surface mass balance mostly relies on reanalysis products or climate model simulations. The ability of models to reproduce the precipitation field at the regional and continental scales not only depends on the simulation of the atmospheric dynamics over the Southern Ocean and of the advection of moisture towards the ice sheet, but also on the representation of the microphysical processes that govern the formation and growth of ice crystals and snowflakes. This presentation reviews recent studies to stress the importance and challenges of evaluating the precipitation microphysics over Antarctica in climate models. It also discusses how recent observational campaigns including ground-based remote-sensing instruments can help pinpoint key processes that should be represented in models. We then present tangible examples of evaluation and improvement of microphysical schemes in the Polar WRF model thanks to radar and lidar observations acquired near Dumont d’Urville and Mawson stations on the Antarctic coast. Particular attention is devoted to three processes : i) the sublimation of snowfall within the katabatic layer that considerably reduces the amount of precipitation that actually reaches the surface ; ii) the snowflake aggregation responsible for rapid depletion of crystals within clouds ; iii) the generation of supercooled liquid water in frontal clouds that leads to crystal/snowflake riming. Such studies, albeit preliminary, could pave the way for further evaluations of clouds and precipitation in climate models in different Antarctic contexts, especially in the cold and pristine atmosphere of the Plateau.

How to cite: Vignon, É., Gehring, J., Alexander, S. P., Sotiropoulou, G., Besic, N., Jullien, N., Planat, N., Madeleine, J.-B., and Gerber, F.: Microphysics of Antarctic precipitation in climate models : recent advances and challenges, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2850, https://doi.org/10.5194/egusphere-egu2020-2850, 2020

Comments on the presentation

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Presentation version 1 – uploaded on 27 Apr 2020
  • CC1: Comment on EGU2020-2850, Heike Kalesse, 06 May 2020

    Hi Étienne, on slide 3 you show the comparison of accumulated precip. fom Pluvio2 and MRR. Which MRR range gate height did you choose for the comparison? Also, down to which temperature do you typically observe supercooled liquid at DDU? thanks, Heike

    • AC1: Reply to CC1, Étienne Vignon, 06 May 2020

      Dear Heike,

      thanks a lot for your interest. For precipitation estimations from MRR data, we use the lowest reliable radar gate (z=300 m a.g.l.). In addition to intrinsic biases associated to the Z-S relationship used, intense low-level sublimation within this 300-m deep layer can explain some of the discrepancies between Pluvio and MRR estimations (sublimation does occur during this event, please see for more details: https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2019JD031028 )

      Regarding the graph showing supercooled liquid water, note that those data come from measurements above the Aurora Australis ice breaker near Mawson station (study leaded by Simon Alexander, AAD).  Results should be presented in a forthcoming publication but in a nutshell SLW layers can be found in boundary layer clouds, embedded within deep nimbostratus associated to the passage of warm fronts or at the top of turbulent altocumulus.

      For Dumont d'Urville, I did not work personally on the characterization of SLW but Claudio Duran-Alarcon and colleagues deployed a lidar there for this purpose. The lidar was operational for several months and statistic of SLW occurrence are presented in Claudio's thesis (pp 52 to 58):

      https://tel.archives-ouvertes.fr/tel-02452286/document

      SLW is mostly detected between 1000 and 2500m i.e. within boundary-layer clouds in the cold sector of cyclones or even sometimes in the warm sector. But higher SLW layers (~3000-4000m) can also be detected within nimbostratus associated to warm fronts. SLW formation is possibly linked with the lifting dynamics of the  warm conveyor belt .

      I hope this answers your questions. Please feel free to ask if you want further info/details.

      Thanks again for your interest,

      Étienne

       

      • CC3: Reply to AC1, Heike Kalesse, 12 May 2020

        Salut Étienne, thanks for your detailed response and for pointing me to some literature with more info that.

        bests,

        Heike

  • CC2: Comment on EGU2020-2850, Marie G. P. Cavitte, 11 May 2020

    Hi Etienne! It's been a while!

    I was there during the chat, but needed some time to digest the information to ask you this: I don't understand how post-precipitation virga form ? It might be a side question to the main point of your presentation but I got curious!

    Thanks! - Marie

    • AC2: Reply to CC2, Étienne Vignon, 12 May 2020

      HI Marie,

      I am glad to hear from you and thanks a lot for your interest. Post-precipitation virga occurs during the final phase of a precipitation event. It is some weak precipitation generated in the tail of the warm sector. As precipitation intensity is weak and katabatic  winds are strong, the snowfall if often totally sublimated.

      I hope this answers your question.

      All the best, and let's keep in touch,

      Étienne