1. Giant Raindrops in mid-latitude Cumuli
Jeffrey French and David Leon, University of Wyoming
Sonia Lasher-Trapp and Daniel Moser, Purdue University
Alan Blyth and Lindsay Bennett, University of Leeds, UK
Alexei Korolev, Environment Canada
Phil Brown, UK MetOffice

2. COnvective Precipitation Experiment (COPE)
UK-led COPE campaign:
to study full array of interacting processes in cloud development from BL convergence lines to development of precipitation (over-arching COPE objective) focusing on understanding and improving NWP for heavy precipitating events, possibly leading to flash flooding.
July – August, summer 2013
SW England
3 aircraft, ground-based X-band radar, mobile sounding systems, rainguage network, UK Metoffice operational radar network
1 May, 2014
EGU-2014; Vienna

3. US contingent specific objectives- Understanding the effect of different microphysical pathways on precipitation formation
Motivation:
to investigate how changes in the relative strengths of various microphysical pathways affect precipitation formation.
Of particular interest is how differences in the strength of the warm rain process impact, directly and through ice multiplication, the development of convective precipitation.
Schematic illustration of microphysical pathways active in a mixed phase convective cloud

4. COPE field campaign ASSETS UWKA w/ WCR & WCL NCAS X-Band Radar
3 bulk CLWC probes
2 droplet spectra probes
Two particle imaging probes
NCAS X-Band Radar
Reflectivity/Doppler
Dual-Polarization
Clear air/cloud sampling

5. Highlights/surprises from COPE
Ubiquity of warm rain, from shallow clouds leading to very high reflectivity/heavy rain;
Range of cloud droplet concentrations and the large fraction of cases with relatively high droplet concentrations…in excess of 350 cm-3 upto 1000 cm-3;
Observation on one day of very large rain drops—lofted high in the clouds (>3 km above cloud base) within high CLWC cores

6. Previous Observations of Large Raindrops
Theoretical studies suggest most raindrops will breakup at diameters from 3-5 mm
Observations of larger drops (rare) have been made—hypotheses have been proposed including need of ultra-giant aerosol, ‘protected’ cores that minimize raindrop/drizzle drop interactions, etc
Previous Observations--
Hobbs and Rangno (2004) (at or below cloud base)
8.8 mm Brazilian forest, biomass burning
6-7 mm Marshall Islands, clean environment, low NC
Rauber et al (1991) Hawaiin Rainbands <2 km
4-8 mm; 4-5 mm were “common” multiple observations >6 mm on multiple days

7. Aug 02 Observations
48 cloud penetrations between 0 and -13 DegC level (2100 – 3500 m above cloud base)
Large updrafts m/s common in freshest turrets
Maximum CLWCs 3 – 4 g/m3, 90 – 95% adiabatic – generally lower in cloud and associated with highest Nc’s (600+ /cm3)
Concentration of precipitation particles (>0.2 mm) low throughout entire day (max few L-1), although LARGE precipitation particles (3-6 mm raindrops) were observed
Max NC ~650 /cm3

8. Aug 02 Case 1 2 Penetrations at ~-7C in 2.5 minutes

9. Aug 02 Case 1
1420: Three minutes after second penetration by UWKA. Top to 6+ km (cutoff by radar), elevated reflectivity, but ZDR column has collapsed. New growth at further range
1411: Two – half minutes prior to first penetration by UWKA – somewhat elevated ZDR, top of cloud cutoff from radar. Top < 4 km (level of UWKA at that time)
1415: One minute after time of first penetration (and during time of second) by UWKA– top to ~5 km , elevated ZDR column to above 4 km, highest reflectivity at 4 km

10. Aug 02 Case 1 Cloud Pass #1: 141350 UTC 13 m s-1 updraft 3 g m-3 CLWC
Up to 1 mm drops observed in middle of cloud
TwoDP conc < 1 L-1

11. Aug 02 Case 1
1.6 mm
6 mm
6 mm

12. Aug 02 Case 1 Cloud Pass #2: 141630 UTC 17 m s-1 updraft 2 g m-3 CLWC
Up to 8 mm (!) drop observed in middle of cloud
TwoDP conc 2-4 L-1

13. Aug 02 Case 1
1.6 mm
1.6 mm
1.6 mm
6 mm

14. Preliminary Attempts at Modeling
OneD modeling to investigate evolution of droplet spectrum and possible onset of warm rain
How to explain large (any?) raindrops in such rapid ascent??—mixing from previous thermals??

15. Direction Forward
More detailed modelling—several days with fewer cloud droplet number resulting in greater production of warm rain—BUT NO LARGE RAINDROPS.
The time of the ‘elevated’ ZDR is quite short—does this imply that majority of growth (at least early) was low in cloud (< 3 km)? The first aircraft pass indicated drops no larger than 1 mm…
Drops 2-3 mm were common on this day—but seemed to occur only within clouds with updrafts >10 m s-1 – investigate interplay between importance of lofting (holding drops up) and rapid ascent of thermal supplying ample CLW for accretional growth.

16. QUESTIONS?