Clouds and storms 1. The air-mass thunderstorm 2. Severe storms ATOC 4720 class21

Cirrus clouds

Cirrostratus: halos

A question from Tom: atmospheric stability : conditionally unstable IMPORTANT:

Dry lapse rate and T profile [Derive on the blackboard]

Saturation lapse rate and T profile

Height (z) Temperature (T) Td Ts FB FG Archimedes’ principle: Acceleration of air parcel Tobs

1. The air mass thunderstorm:isolated

Air mass thunderstorm character Isolated thunderstorm; Occurs in warm and humid regions: tropics and warm marine air-masses drift to middle latitude (say,air from the Gulf Stream); Life cycle: Self destructing mechanism-- downdraft counteracts updraft; Weak or no vertical shear in winds;

2. Severe thunderstorms Occur only in convectively unstable situation; Considerable vertical shear; Downdraft reinforce updraft; Squall lines; multicell storms, supercell storms

Squall lines

Individual cumulonimbus towers (close to each other) are often arranged in long lines; gusty surface winds--squall lines; Often occur in summer: West Africa, south of the Sahara, and mid-latitude lands, including central and eastern US;

Squall lines Conditions, structure, and development: Vertical wind shear; Convectively unstable; Moves with a speed of winds in middle troposphere: so it takes Over the air in the prestorm environment at low levels, while it acts as a massive, slow-moving obstacle to The winds in the upper troposphere; Structure: see figure: downdraft formation, Anvil formation, Mamma; Updraft and downdraft reinforce each other; Surface wind gust 25m/s;

Right-moving multicell storms

Supercell thunderstorm Hails Tornado