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Surface-Based Remote Sensing of Clouds during ASCOS

This study utilizes various data sets including millimeter cloud radar, ceilometer, radiosondes, and microwave radiometer to retrieve cloud type, microphysics, vertical velocity, turbulence, and cloud summary statistics. The study focuses on low-level mixed-phase clouds and their interactions with the boundary layer.

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Surface-Based Remote Sensing of Clouds during ASCOS

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  1. Surface-Based Remote-Sensing of Clouds during ASCOS Matthew Shupe Ola Persson Paul Johnston Cassie Wheeler Michael Tjernstrom Univ of Colorado, NOAA and Stockholm Univ.

  2. Data sets Millimeter Cloud Radar cloud id, boundaries, phase Ceilometer cloud id, base Radiosondes temperature Microwave Radiometer liquid water path 60-GHz Radiometer temperature

  3. Retrieved Products: Cloud type • Cloud type classification • Utilizes phase-specific signatures from radar, ceilometer, microwave radiometer, radiosondes • Provides a mask of cloud “phase” type

  4. Retrieved Products: Cloud microphysics Ice Retrievals Ice mass is derived using a radar reflectivity power law relationship while particle size is related to radar-measured velocity Ice particle size Liquid droplet size Ice water content Liquid water content Liquid Retrievals Assume “adiabatic” profile computed with active sensor cloud boundaries and temperature profile, constrained by microwave radiometer-derived LWP Ice water path Liquid water path

  5. Retrieved Products: Vertical velocity and turbulence Layer-averaged vertical velocity, 5-pt smooth • Dynamics Retrievals • Vertical velocity is derived from radar Doppler spectra using small liquid droplets as tracers of air motion • Turbulent dissipation rate is related to the time variance of radar Doppler velocity Vertical velocity Turbulent dissipation rate

  6. Cloud Summary Statistics Lots of low clouds, most of which were “mixed-phase” (ice crystals falling from a liquid cloud layer)

  7. Cloud Summary Statistics Weak diurnal cycles in low-level mixed-phase clouds and LWP

  8. Case Study Example 29 August 2008 Cloud Radar Moments • From the Cloud Radar Perspective • Low-level mixed-phase stratocumulus (ice falling from liquid cloud layer) • Brief mixed-phase strato/alto-cumulus • Multiple high cirrus clouds and a suggestion of possible liquid water at times.

  9. Case Study Example 29 August 2008 60-GHz Potential Temperature and Buoyancy Profiles Strong inversion at about 800 m which limits the vertical cloud extent Stable layer decouples cloud from surface for first ½ of day Second ½ of day appears to be well-mixed from the surface up to the cloud at 700-800m

  10. Case Study Example 29 August 2008 Retrieval Results: Multilayer Cloud Effects 1) Upper layers from 11 – 16 inhibit cloud top radiative cooling by lower layer. 2) As a result, shallow convection, turbulence, ice production, and (probably) liquid production all decrease in lower cloud layer. 3) Circulations and turbulence are significant in upper layer because it can radiatively cool to space.

  11. Case Study Example 29 August 2008 • Retrieval Results: • BL-Cloud Interactions • During first ½ of day (decoupled • cloud and surface): • Relatively more ice than liquid production. • Thinner liquid layer. • Turbulence decreases towards surface. • During second ½ of day (well-mixed): • Less ice production and more liquid water • Thicker liquid layer. • Turbulence constant towards surface

  12. Case Study Example 29 August 2008 1 2 3 • Examine Profiles at 3 times • Decoupled • Multi-layer • Well-mixed

  13. 1) Decoupled • Turbulence profile suggests cloud top radiative cooling • Lots of ice Case Study Example 29 August 2008 • 2) Multi-layer • Upper layer turbulence shows radiative cooling • Lower layer turbulence suggests surface forcing • Less ice production in lower layer than upper Average profiles • 3) Well-mixed • Turbulence profile suggests contributions from both surface and radiative cooling

  14. Case Study Example 29 August 2008 1) Decoupled: 0.5 -2 km scales 3) Well-mixed: 0.5 -2 km, stronger 2) Multilayer, lower Similar size but weaker 2) Multilayer, upper Smaller scale motions

  15. Case Study Example 29 August 2008 Focus on Circulations during “Well-Mixed” period Broad updrafts and narrow downdrafts on scales of 1-2 km Higher turbulence near strong down-drafts Cloud ice forms in updrafts No clear relationship between LWP-IWP or LWP-updraft but the LWP does increase as the liquid layer thickness increases

  16. Conclusions • Rich cloud data set • Provides detailed perspective on cloud-BL interactions • Nice opportunities for interactions with other groups surrounding retrieval validation, cloud-aerosol interactions, cloud-BL characterization. Thanks!

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