Uplift of low-level air in deep convection Geraint Vaughan

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

Intercomparison flights AD12 – AE10 AD28 – AE Dornier minus Egrett CO, ppbv Difference, ppbv Time, h

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

Sharp fall in upper- level CO during December

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

Monsoon break (5): reversed vertical gradient

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

Sharp decrease in December due to change in air mass origin

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

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

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

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)

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 * Mean background >10 km Anvil Enhancemen t * Mean from 1-3 km Vertical difference for height 2 km Use Egrett descent profile rather than ascent because of problem with Dornier intercomparison.

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

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

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

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

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