1. ATOC 4720 class19 • Thunderstorms 1. Growth of clouds droplets in warm and cold clouds 2. Charge generation 3. Lightning and thunder

2. 1a. Growth of droplets in warm clouds Clouds lie completely below warm clouds; Droplet grow: (1) condensation in supersaturated environment; (2) colliding and coalescing;

3. R>r : grow

4. Heterogeneous: Aerosol: grow 10 (uniform) Collision & coalescence (important) (a few mm);

5. 1b. Growth in cold clouds Clouds extend above 0C, called cold clouds; Can contain: supercooled droplets & ice particles Mixed clouds Growth: (1) homogeneous nucleation (water & ice), heterogeneous nucleation (aerosol); (2) riming: hailstone--ice colliding with Supercooled droplets (quickly grow); Riming to a certain stage----graupel; Hailstones: extreme; 13cm diameter,0.5kg; Common: 1cm; rimming too quick: above 0C-- Water content

6. 2. Charge generation

7. Theories Thermoelectric effect in ice (1&2) T- degree C; V--mV

8. Theory 1

9. Theory 2

10. Theory 3

11. 3. Lightning and thunder Dielectric breakdown: V>3MV/m (dry) V>1MV/m Moist with 1mm in radius;