GEOG 111 1st Edition Lecture 33 Outline of Last Lecture I. Thunderstorms (cont’d)a. Characteristicsb. Developmentc. Typesd. Geographic patternsOutline of Current Lecture I. Thunderstorms (cont’d)II. Review for examCurrent LectureI. Thunderstorm hazardsa. Steps in lightning formationi. Because of updraft/downdraft, positive charges in upper part of the cloud (where the Bergeron process is happening) and negative charges at the bottom part of the cloud1. Negative charges are attracting to the positive charges on the ground2. Air between bottom of the cloud and the ground has trouble conductingelectricitya. Air is a very good insulator so electricity doesn’t want to travel from cloud to ground so charge concentration becomes even greaterb. Negative ionizing path from the bottom of the cloud and positive ionizing path going up (in multiple paths) going from the ground upward3. Tremendous draining of negative charges from clouda. Conductive path establishedb. Return stroke- Rapid movement of electricity from bottom part of cloud to the groundi. This is the current that can kill peopleb. Very unstable atmosphere, bubbles of air convecting upward very rapidly, lots of precipitation at top of the cloud, in conjunction with downdraft right beside iti. More lighting when atmosphere is unstable and air is going upward in a convective mannerc. Types of lightningi. Cloud to ground lightning1. (Described above)ii. Cloud to cloud1. Between two clouds or within a single cloudThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.iii. Bolt from the blue1. Starts from surface and meets cold upper parts of the cloud2. Very unusuald. Where is lightning most likely to hit?i. Higher placesii. Metal objects are more likelye. Safetyi. Inside a house away from windows and not in the shower1. Water and metal pipes are conductiveii. If your skin tingles or your hair stands up, lightning is eminentf. Thunder- compression wave (sound wave) created by the intense heat of the lightning and rapid expansion of the airi. There is a 5 second difference between light seen and thunder heard for each mile of distance; this allows you to calculate distance from the stormii. What factors control the sound and loudness of thunder?1. Clouds muffle sound wave2. Heat lightning is not due to heat necessarily, you’re seeing a thunderstorm from far away and the thunder dissipates iii. Microburst1. Cover a small area2. Short duration3. Significant threat to aviation4. A downdraft (sinking air) that comes out of a storm in the very beginning that is less than 2.5 miles in scaleiv. Hail1. Largest hailstones we see loop multiple times2. Two factors that control the occurrence and size of hailstones:a. Strength of updraftb. Freezing leveli. Areas of higher elevation get more hailii. We get more hail in spring because freezing level is lowerII. Review for exama. When looking at a surface mapi. What direction are winds blowing from?1. Look for nearest isobars assume 45 degree turning of winds toward lower pressureii. What location is experiencing overrunning precipitation?1. Ahead of warm front2. 4 frontal3. 3 wrap aroundiii. Cold sector1. In front of cold front, behind warm frontiv. Winds don’t blow in high pressure1. Spacing between isobars is greatest so winds are weakestb. When looking at 500 mb mapi. Wave cyclones form where there is rising air (you have to remove air from bottom of column)ii. Air sinks immediately downstream of a ridge1. At the surface we would expect an anticyclone or a high pressure systemiii. What direction are winds blowing?1. Blow parallel to lines2. West to east3. Geostrophic winds (well above the surface)c. Be able to recall connections between upper level divergence, rising air and surface pressure
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