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Uplift of low-level air in deep convection

Uplift of low-level air in deep convection. Geraint Vaughan. Example of CO profile. Convective outflow plumes. *. Mean CO out of cloud above 10 km. High variability at low levels (biomass burning). Median CO 1-3 km from Dornier. *. Intercomparison flights. Dornier minus Egrett CO, ppbv.

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Uplift of low-level air in deep convection

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  1. Uplift of low-level air in deep convection Geraint Vaughan

  2. Example of CO profile Convective outflow plumes * Mean CO out of cloud above 10 km High variability at low levels (biomass burning) Median CO 1-3 km from Dornier *

  3. Intercomparison flights Dornier minus Egrett CO, ppbv 25 20 AD12 – AE10 15 10 Difference, ppbv 5 0 AD28 – AE30 -5 13.0 12.6 13.4 12.2 Time, h

  4. Biomass burning period (1) and pre-monsoon(3): CO decreases strongly with height

  5. Sharp fall in upper-level CO during December

  6. Monsoon period (4): no vertical gradient – strong vertical mixing

  7. Monsoon break (5): reversed vertical gradient

  8. Can we explain background changes by long-range transport? • 3-D kinematic back-trajectories calculated from each flight section out of cloud above 200 mb • Most trajectories had ascended from low level in the past 10 days • Point where trajectory ascended through 500 mb surface plotted together with measured background CO from Egrett

  9. Sharp decrease in December due to change in air mass origin

  10. Flights through anvil outflow November 16 (left hand panel): CO enhanced in anvil outflow February 6 (right hand panel): CO reduced in anvil outflow Green/Yellow denotes cloud

  11. Where does the anvil air come from? Anvil peaks in CO above 10 km all less than 110 ppbv Boundary-layer outflow at 8 km? Boundary-layer air all > 100 ppbv

  12. Same for AE25 Anvil peaks in CO above 10 km around 55 ppbv Boundary-layer air > 60 ppbv

  13. Definition: Anvil enhancement Inferred out-of cloud CO concentration, by linear interpolation of measured background values A A: Enhancement of CO in the anvil (negative for this flight)

  14. Definition: Vertical Difference • Calculate average CO in 2 km blocks on Egrett descent profile, from 0 – 8 km • Calculate difference between these averages and the mean background above 10 km • Call this the vertical difference Anvil Enhancement * Vertical difference for height 2 km Mean background >10 km Use Egrett descent profile rather than ascent because of problem with Dornier intercomparison. * Mean from 1-3 km

  15. Method • Calculate anvil enhancement for each flight • Calculate vertical difference for seven vertical intervals: 0-2, 1-3, … 6-8 km, for each flight • Plot against each other • Calculate correlation coefficient for each set of vertical differences

  16. Mean anvil enhancement vs. vertical difference, all flights Mean anvil enhancements << vertical differences – suggests mixing 1 : 1 line Line of symbols represents one flight

  17. Correlation coefficients Correlation coefficients increase slowly to a peak at 4-6 km then decrease sharply

  18. Maximum anvil enhancement Maximum anvil enhancements similar in magnitude to vertical differences Max correlation again around 5 km

  19. Conclusions • Trajectory calculations consistent with background upper-level CO measurements: impact of local convection small except in monsoon • Maximum anvil enhancement suggests that uplift from mid-levels dominates anvil composition during pre-monsoon and monsoon break

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