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SE Pacific Sc Research at UW

SE Pacific Sc Research at UW. Chris Bretherton, Rob Wood, Peter Caldwell, Kim Comstock April 23, 2004. Recent work at UW. Patches of open cells (POCs) Inferring MBL structure by combining knowledge from satellites and reanalysis Diurnal cycle of subsidence, entrainment.

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SE Pacific Sc Research at UW

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  1. SE Pacific Sc Research at UW Chris Bretherton, Rob Wood, Peter Caldwell, Kim Comstock April 23, 2004

  2. Recent work at UW • Patches of open cells (POCs) • Inferring MBL structure by combining knowledge from satellites and reanalysis • Diurnal cycle of subsidence, entrainment.

  3. The first satellite remote sensor - Tiros 1 TV Camera in space Mesoscale cellular convection

  4. C-band reflectivity and radial velocity Mesoscale wind fluctuations related to drizzle cells Radial velocity fluctuations Radar reflectivity

  5. The “POCS” mystery Pockets Of Open Cells (POCS) are frequently observed in otherwise unbroken Sc.Their cause is unknown POCS

  6. 100km MODIS 250m visible imagery

  7. POCS regions drizzle more Figure by Kim Comstock/Rob Wood

  8. POCS and cloud droplet size MODIS brightness temperature difference, GOES thermal IR, scanning C-band radar Figure by Sandra Yuter/Rob Wood

  9. Climatology of open and closed cellular regions…role of deepening-induced Cu-coupling vs. drizzle?

  10. POCS and drizzle – summary • POCS last for days, and are associated with large cloud droplet effective radius and enhanced drizzle. • Patchy drizzle evaporation in POCs drives spreading mesoscale cool pools, reinforcing cellular structure • Drizzle scavenging promotes aerosol depletion in POCs.

  11. MBL depth, entrainment, and decoupling

  12. Methodology (Wood, Park, Bretherton) • Independent observables: LWP, Ttop, SST • Unknowns: zi, q (= ) • Use COADS climatological surface RH and air-sea temperature difference • Use NCEP reanalysis free-tropospheric temperature and moisture • Iterative solution employed to resulting non-linear equation for zi

  13. Mean MBL depth (Sep/Oct 2000) NE Pacific SE Pacific

  14. Mean decoupling parameter q Decoupling scales well with MBL depth

  15. q vs zi-zLCL

  16. Deriving mean entrainment rates • Use equation: we=uzi+ws • Estimate ws from NCEP reanalysis • Estimate uzifrom NCEP winds and two month mean zi

  17. Mean entrainment rates Entrainment rate [mm/s]◄ NE PacificSE Pacific ►Subsidence rate [mm/s]

  18. Cross section through SE Pacific stratocumulus sheet

  19. Diurnal subsidence wave - ECMWF • Daytime dry heating leads to ascent over S American continent • Diurnal wave of large-scale ascent propagates westwards over the SE Pacific at 30-50 m s-1 • Amplitude 0.3-0.5 cm s-1• Reaches over 1000 km from the coast, reaching 90W around 15 hr after leaving coast

  20.  0.05 cm s-1 zi/t + u•zi= we - ws NIGHT DAY NIGHT DAY we dzi/dt ws EPIC 2001 [85W, 20S]Diurnal cycle of subsidencews, entrainmentwe, andzi/t swe=0.24cm s-1 sws=0.26 cm s-1 szi/t=0.44 cm s-1 Conclusion: Subsidence and entrainment contribute equally to diurnal cycle of MBL depth

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