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

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

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

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

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

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

Aug 02 Observations 48 cloud penetrations between 0 and -13 DegC level (2100 – 3500 m above cloud base) Large updrafts 12-20 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

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

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

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

Aug 02 Case 1 1.6 mm 6 mm 6 mm

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

Aug 02 Case 1 1.6 mm 1.6 mm 1.6 mm 6 mm

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??

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.

QUESTIONS?