1. Thunderstorms

2. Review of last lecture 1.Two types of lightning (cloud-to-cloud 80%, cloud-to- ground 20%) 2.4 steps of lightning development. 3.How fast does thunder travel? 4.Climate impacts of lightning: nitrogen cycle, ozone, wildfire 5.Lightning safety

3. Convective systems Tornadoes: about 100-600 m, last 1 minute to 1 hour Tornadoes: about 100-600 m, last 1 minute to 1 hour Thunderstorms: about 10 Km, last 10 minutes to a couple of hours. 3 types: ordinary, multicell, supercell Thunderstorms: about 10 Km, last 10 minutes to a couple of hours. 3 types: ordinary, multicell, supercell Mesoscale convective systems (MCSs): A cloud system that occurs in connection with an ensemble of thunderstorms and produces a contiguous precipitation area on the order of 100 Km or more in at least one direction, and often last for several hours to a couple of days. Mesoscale convective systems (MCSs): A cloud system that occurs in connection with an ensemble of thunderstorms and produces a contiguous precipitation area on the order of 100 Km or more in at least one direction, and often last for several hours to a couple of days.

4. Thunderstorms A storm containing lightning & thunder A storm containing lightning & thunder Convective; form when warm, humid air rises in conditionally unstable environment Convective; form when warm, humid air rises in conditionally unstable environment The warmer the rising air parcel is relative to environment, the more buoyant force is driving it upwards (stronger convection) The warmer the rising air parcel is relative to environment, the more buoyant force is driving it upwards (stronger convection) Trigger to start uplift: warming sfc, terrain (orography), converging sfc winds, frontal zones, divergence aloft (or combination) Trigger to start uplift: warming sfc, terrain (orography), converging sfc winds, frontal zones, divergence aloft (or combination)

5. Three stages have been identified in ordinary thunderstorms: a)DEVELOPING: unstable atmosphere, vertical updrafts keep precipitation suspended b)MATURE:entrainment of dry air that causes cooler air from evaporation, triggering downdrafts and falling precipitation and gust fronts b)MATURE: entrainment of dry air that causes cooler air from evaporation, triggering downdrafts and falling precipitation and gust fronts c)DISSIPATING:weakening updrafts and loss of the fuel source after 15-30 minutes. c)DISSIPATING: weakening updrafts and loss of the fuel source after 15-30 minutes. Thunderstorms I. Ordinary Storms

6. An ordinary thunderstorm

7. Cool downdrafts leaving a mature and dissipating storm may offer relief from summer heat, but they may also force surrounding, low-level moist air upward. Hence, dying storms often trigger new storms, and the successive stages may be viewed in the sky. Thunderstorms II. Multicell Storm

8. A Multicell Thunderstorm

9. Video: Supercell thunderstorm http://www.youtube.com/watch?v=UBTb5 Yd20cM http://www.youtube.com/watch?v=UBTb5 Yd20cM http://www.youtube.com/watch?v=UBTb5 Yd20cM http://www.youtube.com/watch?v=UBTb5 Yd20cM

10. Storms producing a minimum of a) 3/4 inch hail and/or b) wind gusts of 50 knots and/or c) tornado winds, classify as severe. Thunderstorm III. Supercell Storm

11. Formation of supercell thunderstorms 1. Before thunderstorms develop, a change in wind direction and an increase in wind speed with increasing height creates an invisible, horizontal spinning effect in the lower atmosphere. 2. Spinning horizontal vortex tubes created by surface wind shear may be tilted and forced in a vertical path by updrafts. This rising, spinning, and often stretching rotating air may then turn into a mesocyclone. 3. Most strong and violent tornadoes form within this area of strong rotation.

12. Vertical structure of a supercell thunderstorm In ordinary storms, the downdraft and falling precipitation cut off the updraft. But in supercell storms, winds aloft push the rain away and the updraft is not weakened and the storm can continue maturing and maintain its structure for hours. In ordinary storms, the downdraft and falling precipitation cut off the updraft. But in supercell storms, winds aloft push the rain away and the updraft is not weakened and the storm can continue maturing and maintain its structure for hours.

13. Cloud structure of a supercell thunderstorm

14. Tornado A Supercell Storm in Texas

15. Horizontal structure of a supercell thunderstorm

16. Radar echo of a supercell

17. Satellite image of a supercell

18. Video: Development of a supercell thunderstorm http://www.youtube.com/watch?v=36vGiE 5JQzs (90 min -> 2 min lapse) http://www.youtube.com/watch?v=36vGiE 5JQzs (90 min -> 2 min lapse) http://www.youtube.com/watch?v=36vGiE 5JQzs http://www.youtube.com/watch?v=36vGiE 5JQzs

19. Different types of supercell thunderstorms Low precipitation Low precipitation High precipitation High precipitation

20. Effects of supercell thunderstorms Large hails Large hails Damaging winds Damaging winds Deadly tornadoes Deadly tornadoes Flooding Flooding Dangerous cloud-to-ground lightning Dangerous cloud-to-ground lightning

21. Global distribution Asia Asia Australia Australia Europe Europe North America North America South Africa South Africa

22. Video: Multiple tornadoes from one supercell http://www.youtube.com/watch?v=FPfO- yjomig http://www.youtube.com/watch?v=FPfO- yjomig http://www.youtube.com/watch?v=FPfO- yjomig http://www.youtube.com/watch?v=FPfO- yjomig

23. Summary 1.The general size and lifetime of mesoscale convective systems, thunderstorms and tornadoes 2.3 types of thunderstorms. 3.3 stages of the ordinary thunderstorms. 3.3 stages of the ordinary thunderstorms. Downdraft and falling precipitation cut off the updraft. 4.Formation of multi-cell thunderstorms. Downdrafts initiate new thunderstorms in nearby regions. 1.3 stages of the supercell thunderstorms. 1.3 stages of the supercell thunderstorms. Winds aloft push downdraft/precipitation away and the updraft is not weakened.