Chapter 5

# Chapter 5 - Chapter 5 Atmospheric Stability ATOC 1050 I...

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Chapter 5 – Atmospheric Stability ATOC 1050 I. Concept of stability: A. Stable – if you give air a vertical “push”, it falls back into place or spreads horizontally. B. Unstable - if you give air a vertical “push”, it accelerates away from its initial position. C. Neutral – if you give the air a vertical “push”, it will remain in its new position. D. What is a “push”? 1. Mechanical push – cold fronts, wind shifts, orographic, low pressure trough, stationary fronts, etc. 2. Thermodynamic push– day time heating (warm the surface) E. Adiabatic process = heating/cooling due only to compression/expansion of air. Important – NO HEAT ENERGY ADDED! F. Lapse rate = temperature change with height. 1. Dry adiabatic lapse rate (DALR) = 10 ° C/km [Use DLR for dry air (no clouds)]. 2. Saturated (or moist/wet) adiabatic lapse rate (SALR) 2245 6 ° C/km [Use SLR when air is saturated (clouds)]. Why is the SLR less than the DLR? 3. Environmental lapse rate (ELR) = temperature measured by the radio/rawinsondes. That is, how the temperature is actually changing with height. This can vary from hour to hour, day to day which is why it is measured twice a day! Example of 7 ° C/km ELR and a -5 ° C/km ELR: 1

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II. Why do we care about stability? 2
A. Unstable air is required for thunderstorms including severe thunderstorms. B. Thunderstorms are severe if they have 1 or more of the following: 1. Hail ¾ inches in diameter 2. Funnel cloud (a funnel cloud that touches ground is a tornado) 3. Wind gusts 50kts. C. Severe thunderstorms can cause deaths and injuries plus crop and

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Chapter 5 - Chapter 5 Atmospheric Stability ATOC 1050 I...

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