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Sea Salt and Warm Rain: From Observation to Modeling

Explore the relationship between sea salt aerosols and warm rain through observations and modeling, including cloud thermodynamics, aerosol size spectrum, cloud age, entrained air, and more.

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Sea Salt and Warm Rain: From Observation to Modeling

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  1. Sea-salt and warm rain – from observation to modelingJorgen B. JensenNCAR/EOL

  2. Most warm-cloud model calculations are based on incompleteobservations, e.g. Assumed or partially measured aerosol spectrum No observed cloud agePresent case is not perfect, but it does have: Sub-cloud thermodynamics Sub-cloud “complete” aerosol size spectrum Cloud age Source of entrained air Amount of entrained air Measurement of cloud and drizzle drop spectrum

  3. Thin curve: Cloud water Bold curve: Drizzle water

  4. Sub-cloud air and CCN

  5. MICROPHYSICS PROCESS MODEL DATAComplete CCN spectrum (CCN, ASASP, FSSP)Thermodynamics of cloud-base airCloud age (visual and mean updraft)Source and amount of entrained airMODEL COMPARISON NEAR CUMULUS TOPConcentration with radius > 20 micronDrop spectrum shape

  6. MODEL DESCRIPTIONParcel modelAssume aerosol chemical compositionCondensationGravitational coalescenceDiscrete entrainment (1 event, 1/3 environmental air entrained)Classical homogeneous mixingKinematic updraft (constrained by observations)GILLESPIE (1975) MONTE-CARLO MODEL1 liter air volume205000 individual particles, 50 bins, 20000 categories Millions of coalescence probabilities for each coalescenceSPECIAL: Track history of each aerosol particle

  7. Particle spectra from sub-cloud air, recalculated to give dry aerosol radius. Assume ammonium-bisulfate for small particles, NaCl for large particles.

  8. Aerosol spectra in sub-cloud air (from ASASP and FSSP) compare well with Woodcock’s measurements for 4 m/s.

  9. Move parcel up, then let it remain at observation level. Entrain once, classical homogeneous mixing, dilute and evaporate. Compare predicted and observed drizzle drop concentration.

  10. Sample volume issue: Model volume of about 1 liter. Compare observed drop spectra and model predicted drop spectra for 8, 20 and 40 minutes of model time.

  11. What is a coalescence nuclei?

  12. What sizes do coalescence nuclei have? Which coalescence nuclei form the largest drops? What if we could measure larger aerosols?

  13. Which aerosols contribute most to the precipitation rate?

  14. BASED ON MEASUREMENTS AND MODELING:Surprisingly good match between model predicted drizzle drop concentrations and sizes.This was based on a very simple parcel model.Observations of the giant aerosol spectrum was critical.DO WE NEED TO INCLUDE MORE SOPHISTICATED PHYSICS?Turbulent enhancements to collision kernels?Mixing between different parts of clouds?Inhomogeneous entrainment?DO WE NEED MEASUREMENTS OF GIANT AEROSOL?

  15. GIANT NUCLEI IMPACTOR

  16. In marine air, the giant aerosol concentrations varies by a factor 10000 as a function of wind speed. What is the variation over land and high in the atmosphere?

  17. Glass impaction slide – 50 year old technology Now with automatic analysis. 6.25 x 22 mm x 120 m/s -> 1 cubic-meter in a minute.

  18. Woodcock’s technique, adapted for automation.

  19. Sample cloud base air, environment air and detrained air -> Process verification.

  20. i ACE-Asia: Sample 3 slides on ascent, 3 at high altitude, and 3 on descent. Pass through ITCZ.

  21. 1 pixel = 0.8 micron

  22. Sampled north of Denver during upslope conditions, Oct. 2002. Boundary-layer air.

  23. WARM RAIN PARAMETERIZATION

  24. i Assumption of 100 drops: For a Marshall-Palmer distribution, how many of the largest drops does it take to carry 80% of the precipitation flux? Somewhat arbitrarily choose 100 drops per m3.

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