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Basis of Thunderstorms.docx

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Langara College
GEOL 2207

Thunderstorms 1. Be wary of the main storm hazards. 
 a. Thunderstorms can create many hazards to life and property: lightning, tornadoes, hail, downpours and local flooding, and downburst and gustfronts (we will learn about these in later vignettes). 2. Recognize thunderstorms, be able to identify thunderstorm components, and explain how they evolve. 
 Looks like anvil or mushroom.Thick clouds. Sometimes a very large, rotating single-cell thunderstorm forms, called a supercell Tstorm. They can cause tornadoes, large hail, frequent lightning, heavy rain, strong wind 3. Explain how storms get their energy from the Sun.
 a. Solar energy is absorbed at 3 different heights: thermosphere (top), stratopause (middle) and earth surface (bottom). b. Absorbed sunlight at ground changes to sensible heat (warms the air) -> temperature increases. c. Latent heat (evaporates water from lakes, etc) -> humidity increases. 2 heat sources forms fuel storms. 4. Explain the main characteristics that make a supercell thunderstorm so much nastier than a normal thunderstorm. a. It has one rotating cell, and lasts 30+ minutes due to wind shear. Windshear is from wind speed or direction changes with altitudes, and it will continuously draw humid boundary air as fuel. Mesocyclone is when the whole supercell storm rotates, and cloud continues to spiral around the main updraft, forming the strongest tornadoes. - 5. Be able to recognize thunderstorms in radar and satellite images. a. Weather radar transmits a beam of microwaves into the atmosphere, and "listens" for the faint echo of microwave energy that bounces back off of raindrops. Heavier rain causes a stronger echo, which is often coloured as yellow and red on radar displays. The lighter rain is shown with the blues and greens. The radar image below shows a number of thunderstorms producing spotty heavy rain, with no rain (shown as black in this image) in between b. On visible satellite photos of thunderstorms, you can often see the shadow of the thunderstorm anvil that is cast on the lower clouds or on the ground. The anvils (marking the tops of thunderstorms) in the satellite image below are circled in red. 6. Describe the different types of lightning, how they form, and what happens when they strike something.
 a. Lightning forms because electrical charges build up in thunderstorms, associated with the freezing and collision of cloud droplets and ice crystals (called graupeln). When the electrical potential (i.e., charge difference) between the cloud and ground becomes great enough (a breakdown potential of 3 billion volts / km is needed, for every km length of the lightning bolt), the air ionizes. b. Cloud-to-cloud (IC) lightening: occurs when voltage gradient within a cloud, or between clouds overcomes electrical resistance of air. c. Cloud-to-ground (CG) lightening: occurs when negative charges accumulate in lower portions of cloud. Can be positive or negative. Negative strikes are more frequent, come from cloud base. Positive strikes are less frequent, come from anvil, primary cause of natural wild fires. 7. Explain the behavior of downbursts and gust fronts, and identify their associated cloud & dust features.
 - ✦What: Downburst - cold (dense) air sinking. - ✦Why: Tstorm can create dense air where rain falls; due to •precipitation drag & •evaporative cooling. - ✦Risks: Often invisible, but hazard to aircraft - -------------------------------------
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