Roelof Bruintjes, Sarah Tessendorf, Jim Wilson, Rita Roberts, Courtney Weeks and Duncan Axisa WMA Annual meeting 26 April 2012

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Aerosol affects on the microphysics of precipitation development in tropical and sub-tropical convective clouds using dual-polarization radar and

1 Aerosol affects on the microphysics of precipitation development in tropical and sub-tropical convective clouds using dual-polarization radar and airborne measurements. Roelof Bruintjes, Sarah Tessendorf, Jim Wilson, Rita Roberts, Courtney Weeks and Duncan Axisa WMA Annual meeting 26 April 2012

2 Overall objective CAN CLOUD SEEDING WITH HYGROSCOPIC AND GLACIOGENIC MATERIALS ENHANCE RAINFALL? Queensland and India examples Tessendorf et al., 2012

3 Aerosol and non-aerosol days classification for Mexican hygroscopic seeding data Typical non-aerosol day (<0.1 optical depth) Typical aerosol day (>.1 optical depth)

4 Questions How variable are aerosol and CCN concentrations in a specific region. Which factors determine the concentration and size distributions of aerosols in a specific region. How do these changes affect cloud microphysical and precipitation formation processes in clouds. What are the impacts cloud seeding experiments.

5 Aerosol Variability and sources in Queensland ` HYSPLIT back trajectries Continental and Maritime CCN Aerosol and CCN variations Tessendorf et al., 2012 CCN spectra

6 The effect of forest fires and city pollution and rainfall during past 12 hours Aerosol concentrations as a function of number of hours over land below 2 km, distance from Brisbane, number of forest fires, and rain during the past 12 hours

of number of hours over land below 2 km, distance from

7 Aerosol concentration

Warm rain process (Typical in clouds with cloud bases warmer than 20C in both polluted and clean environments Collision and coalescence of droplets

8 Warm rain process (Typical in clouds with cloud bases warmer than 20C in both polluted and clean environments Collision and coalescence of droplets falling at different terminal velocities leads to raindrop formation Raindrops are millimeters in size Cloud droplets are 100 times smaller in diameter

falling at different terminal velocities leads to raindrop formation

Temperature versus time Images of cloud droplet spectra at 22 January 2009 droplets and drizzle/rain drops

9 Precipitation Processes: OLD example (22, 27 Jan. 2009) Due to warm cloud bases (~20 o C) all clouds initially develop warm rain process Continental cloud Temperature versus time Images of cloud droplet spectra at 22 January 2009 droplets and drizzle/rain drops cloud base Coalescence initiates before cloud top reaches 0 o C Drizzle/rain drops present as cloud rises through 0 o C level Cloud droplet size distributions at cloud base and 0 o C.

10 The cold rain process Co-existence of ice crystals and supercooled droplets leads to rapid vapor growth of crystals, followed in suitable convective clouds by accretional growth (riming), fall-out, and melting as rain Graupel

crystals, followed in suitable convective clouds by

11 Precipitation Processes: Mixed/ice processes initiated by freezing of large drizzle/rain drops and subsequent initiation of natural seeding (ice splintering) process rapidly depleting cloud liquid water content Large drop freezing at ~-5 o C Initiation of ice splintering process Rapid conversion of LWC to ice and precipitation Rapid depletion of LWC inhibiting lightning in these cases LWC versus altitude Temperature versus time 27 January 2009

freezing at ~-5 o C Initiation of ice splintering process Rapid conversion of LWC to ice and precipitation

12 Cloud base heights and warm cloud depths during Queensland project 22 November 2008 High cloud base No large drops at 0C First ice below -12C

13 Microphysical relationships Total peak droplet concentrations (cm -3 ) as a function of standard deviation of the cloud droplet spectra for the 22 cases when penetrations were conducted in deep convection near cloud base in growing nonprecipitating parts of the cloud. Mean diameter of the cloud base doplet spectra as a function of standard deviation of the cloud droplet spectra for the 22 cases when penetrations were conducted in deep convection near cloud base in growing non-precipitating parts of the cloud.

14 Aerosols, CCN and Cloud droplet concentrations (India) High concentrations of droplets due to pollution CCN and aerosol conc.

15 Broadening of cloud droplet spectra by re-circulation CCN effect: Difficult to form rain in clouds

16 Effects on Ice Processes Large drops freezing Secondary Ice Formation Concentrations between 200 to 400L -1 Concentrations: ~5-10L -1 Similar to concentrations of observed large drops TENTIAL INVIGORATION OF CLOUD OWTH DUE TO LATENT HEAT OF EEZING

Concentrations: ~5-10L -1 Similar to concentrations of

17 Polarimetric Radar data collected on: -Continental and maritime storms -Seeded and non-seeded storms -Many stratiform and convective rain events over video disdrometer -sea breeze and terrain initiated and seeded storms -intense hailstorm Reflectivity Velocity Differential Reflectivity

events over video disdrometer -sea breeze and terrain initiated and

18 Randomized seeding by aircraft in clouds that developed above sea breeze front. Highlights: -4 seeded clouds -2 not seeded clouds -several additional nonseeded cells formed along front -All randomized seeding tests conducted within south and north dual- Doppler lobes (yellow circles). -Dynamics, kinematics and microphysical information possible from radar. -Can examine impacts of seeding on downdraft production and outflows. 03:42 UTC 13 February 2008 Sea Breeze Location Decision to Not Seed 03:59 UTC Decision to Seed 03:20 UTC Decision to Seed 03:40 UTC

conducted within south and north dual- Doppler lobes (yellow circles).

19 Direct wind, precipitation rate and particle identification in clouds

20 Differential reflectivity and raindrop sizes

21 Dual Polarization Radar Time height diagrams of radar reflectivity and differential radar reflectivity Wilson et al., 2012

22 Dual Polarization Radar measurements Rain drop size distributions

23 Area Median Mean >10 dbz D0 ZDR of dbz Brandes (km 2 ) two equations Plots of selected variables 22 Jan 2009 Cell 03 AREA Dbz ZDR D Seeding Seeding.50 Seeding :30 02:40 02:50 03:00 03:10 03:20 03:30 03:40 03:50 Time (UTC) 10

24 Results summary Polarimetric results Seeded cell slightly longer life than sister but sister larger; intensity equal, Median Zdr and D0 seem to decrease more than other cells. Other seeded cells acted similar and not evident in non-seeded cells More drizzle and higher level of large drops but more quicker Faster increase in water loading and potentially more sudden and intense downdraft Next steps to look at dual data and cases:

25 Summary There can be large variability in aerosol and CCN concentrations in a region The variations together with cloud base heights and other meteorological factors can influence microphysical processes. These microphysical effects can lead to differences in warm and cold rain formation processes Dual polarization radar data can provide new insights into the microphysical and precipitation formation processes These microphysical effects will also lead to dynamic effects such as cold pool effects and subsequent cloud formation These effects will certainly impacts the responses to cloud seeding to enhance rainfall or mitigate hail. These factors should be considered in the design of both research and operational programs.

26 END

Chapter 8, Part 1. How do droplets grow larger? Cloud Droplets in Equilibrium. Precipitation Processes

Chapter 8, Part 1. How do droplets grow larger? Cloud Droplets in Equilibrium. Precipitation Processes Chapter 8, Part 1 Precipitation Processes How do droplets grow larger? Cloud contain water droplets, but a cloudy sky does not always mean rain. Cloud Droplets in Equilibrium In equilibrium water molecules