Thunderstorms

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

Convective systems Tornadoes: about m, last 1 minute to 1 hour Tornadoes: about 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.

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)

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 minutes. c)DISSIPATING: weakening updrafts and loss of the fuel source after minutes. Thunderstorms I. Ordinary Storms

An ordinary thunderstorm

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

A Multicell Thunderstorm

Video: Supercell thunderstorm Yd20cM Yd20cM Yd20cM Yd20cM

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

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.

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.

Cloud structure of a supercell thunderstorm

Tornado A Supercell Storm in Texas

Horizontal structure of a supercell thunderstorm

Radar echo of a supercell

Satellite image of a supercell

Video: Development of a supercell thunderstorm 5JQzs (90 min -> 2 min lapse) 5JQzs (90 min -> 2 min lapse) 5JQzs 5JQzs

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

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

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

Video: Multiple tornadoes from one supercell yjomig yjomig yjomig yjomig

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.