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Understanding Vertical Motions & Microphysics in Arctic Clouds

This study explores vertical motions and microphysics in Arctic mixed-phase stratus clouds using ground-based observational methods, cloud classification, and a conceptual model. The research focuses on phase balance, boundaries, optical depth, and vertical velocity to enhance our knowledge of cloud dynamics. Results indicate the dominance of liquid over ice in single layer stratus clouds. The study emphasizes the need for new methods and further validation in cloud phase classification and vertical motion retrievals, with radar Doppler spectra playing a crucial role. The conceptual model proposed describes cloud structure in autumn at Barrow, highlighting key gaps in understanding liquid properties.

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Understanding Vertical Motions & Microphysics in Arctic Clouds

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  1. Vertical Motions and Microphysics in Arctic Mixed-Phase Stratus Matthew Shupe With contributions from Pavlos Kollias, Ed Luke, Ola Persson, Greg McFarquhar, Michael Poellot, Ed Eloranta John Daniel, Gijs DeBoer, Chuck Long, Dave Turner Hans Verlinde, Amy Solomon ARM Science Team Meeting 2007

  2. Topics Status of Ground-Based Observational Methods Cloud Classification M-PACE Vertical Motions & Microphysics A Conceptual Model

  3. Status of Ground-based Retrievals Phase Classification Microphysics Radiation Dynamics

  4. Status of Ground-based Retrievals Boundaries LWP IWP Phase Balance Optical Depth Vertical Velocity

  5. The Spectrum of our Knowledge From Ground-based Sensors Certain “Known” Unknown Phase balance (layer) Aerosol profile Phase Classification Ice Re Phase balance (resolved) IWC/IWP Cloud Boundaries LWP LWC No assumption LWC (adiabatic) Liquid Re (thin clouds) Liquid Re (Thick clouds) Ice optical depth Radiative Forcing Liquid optical depth Heating Rate Liquid extinction (thick) Ice extinction Liquid extinction (thin) Vertical Velocity Turbulent dissipation rate Need new methods Need further validation

  6. Cloud Phase Classification MMCR Doppler spectra-based technique Slide from P. Kollias & E. Luke

  7. Small liquid droplets trace vertical air motions Ice Particles Liquid Droplets Correction for spectral broadening W Vertical Velocity Retrieval • Identify cloud liquid • Spectral broadening corrections • Left edge of spectrum plus corrections Assumption: Liquid droplets trace vertical air motions.

  8. Various periodic scales-of-motion Vertically-coherent structures An Example

  9. Aircraft Comparisons at M-PACE Different Air mass?

  10. Liquid dominant Down Up Results from M-PACE: Single layer stratus Mean upward motion in cloud More liquid and less ice than SHEBA

  11. Time Series Analysis Dominant scales: 0.7 – 10 km Dominant scales: 2 – 10 km

  12. -3 -2 -1 0 1 -3 -2 -1 0 1 W [m s-1] W [m s-1] Up Down Cloud Response to Vertical Motions

  13. In Focus Motions at 7, 2, and 0.5 km wavelengths Ice forms in updrafts near cloud top, falls out. Liquid persists throughout cycle, supported by almost complete ice fallout

  14. A Conceptual Model • Updraft • Cloud top lifts • LWC near adiabatic • Ice particle nucleation • Limited ice concentration • IWC maximum near liquid base • RH ~ 100% in cloud layer • Downdraft / neutral • Cloud top descends • LWC sub-adiabatic (evaporation) • Ice particles fall out • IWC negligible • RH < 100% in cloud layer

  15. Representative? Change at the coastline? Barrow

  16. Conclusions • Still some gaps in our abilities: • Most importantly the vertical dist’n of liquid properties • New classification methods: • Radar Doppler spectra are rich with information • Vertical velocity retrievals: • Provide for a better understanding of microphysical-dynamical processes • Conceptual model: • Describes cloud structure in autumn at Barrow

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