Hazardous Weather Detection and Prediction

1. Hazardous Weather Detection and Prediction Kelvin K. Droegemeier University of Oklahoma Week #1, Lecture #2 Thursday, 20 January 2005

2. As a Reminder… • Please send an email to kkd@ou.edu containing the following • Full name (first, last) • Social Security or Student ID Number • Institution • Major field of study • Year in school or title if not a student • Principal email address • Enrollment status (credit, audit, sitting in)

3. Atmospheric Composition Lutgens and Tarbuck, The Atmosphere, 8th edition

4. Atmospheric Composition Seasonal trendrelated to Carbon fixation in plants via the Calvin Cycle

5. Courtesy NCAR

6. Vertical Structure of the Atmosphere 90% of total mass residesin the lowest 10 km 50% of total mass residesin the lowest 5-6 km

7. Vertical Structure of the Atmosphere • Key questions • Why do thunderstorms form in the lower parts? • Do the upper parts have any influence? • What parts do we need to observe, and which variables?

8. The Troposphere • From the Greek tropein, which means turn or change • Ground-level to 10-12 km • Where all weather occurs • Contains 90% of mass and almost all of the H20V • Average lapse rate (-dT/dz) of 6.5 K km–1 • Topped by tropopause (above is isothermal layer) • Little exchange between troposphere and layers above • Typically find a temperature “inversion” (temp increases with height) in lowest 2 km – very stable • Sampled by radiosondes

9. Low-Level Temperature Inversion Rawinsonde

10. The Stratosphere The Stratosphere • 10-50 km in altitude (strato meaning stratified) • T increases dramatically with height (deep inversion) owing to ozone heating • Max ozone location is optimal region for concentration and photochemstry • T continues to increase above max ozone region because of intense molecule excitation at low density and high altitude, and because absorbed energy at high altitudes does not reach lower altitudes • Thunderstorms sometimes penetrate into stratosphere (overshooting top) • Upper limit is stratopause

12. The Mesosphere The Stratosphere • Meso means “middle” • 50-80 km in altitude • Density is very low and ozone concentrations are nil; thus air molecules lose more energy than they absorb and the atmosphere cools with height at a rate of about - 3K km-1 • Coldest temperatures are at the mesopause, the top of the mesosphere – marking the bottom of another inversion

13. The Thermosphere The Stratosphere • 80-200 km altitude • This is an extremely “hot” layer where molecular Oxygen absorbs highly energetic photons • Mean free path is about 1 km • Air would not “feel” warm! • Temperature is measured indirectly, by orbital changes in satellites • Exospheric temperatures vary significantly in time owing to changes in solar activity

14. Other Layers The Stratosphere

15. Back to Our Questions… • Why do thunderstorms form in the lower parts? • Moisture is present • Temperature structure • Do the upper parts have any influence? • Indirectly (tropopause height, large-scale dynamics) • What parts do we need to observe, and which variables? • Troposphere • T, P, dens, moisture, soil temp/moisture, wind, particulates, precipitation…