1. Chapter 1: What is the Mesoscale? Mesoscale energy sources

2. Gage and Nastrom (1985) [shifted x10 to right] Note two spectral extremes: (a) A maximum at about 2000 km (b) A minimum at about 500 km 1 10010 1000 wavelength [km] (1) Scales of atmospheric motion inertial subrange

3. FA=free atmos. BL=bound. layer L = long waves WC = wave cyclones TC=tropical cyclones cb=cumulonimbus cu=cumulus CAT=clear air turbulence From Ludlam (prior to Gage/Nastrom) energy cascade mesoscale Big whirls have little whirls that feed on their velocity; and little whirls have lesser whirls, and so on to viscosity. -Lewis Fry Richardson

4. Scales of atmospheric motion Air motions at all scales from planetary-scale to microscale explain weather: – planetary scale: low-frequency (10 days – intraseasonal) e.g. blocking highs (~10,000 km) – explains low-frequency anomalies size such that planetary vort adv > relative vort adv hydrostatic balance applies – synoptic scale: cyclonic storms and planetary-wave features: baroclinic instability (~3000 km) – deep stratiform clouds size controlled by  =df/dy hydrostatic balance applies – mesoscale: waves, fronts, thermal circulations, terrain interactions, mesoscale instabilities, upright convection & its mesoscale organization: various instabilities – synergies (100-500 km) – stratiform & convective clouds time scale between 2  /N and 2  /f hydrostatic balance usually applies – microscale: cumuli, thermals, K-H billows, turbulence: static instability (1-5 km) – convective clouds Size controlled by entrainment and perturbation pressures no hydrostatic balance note: 2  /f = 12 hours/sin(latitude) = 12 hrs at 90°, 24 hrs at 30°

5. Fig. 1.1

6. Eulerian vs Lagrangian Eulerian time scale t e : time for system to pass, assuming no evolution –t e =L/U, where L is size, U is basic wind speed Lagrangian time scale t l : time for particle to travel through system –for tropical cyclone or tornado, –for sea breezes, –for internal gravity waves, Lagrangian Rossby number: intrinsic frequency / Coriolis parameter –Ro l = 1 for inertial oscillations

7. 1.2 Mesoscale vs. synoptic scale Fig. 1.2 (Fujita 1992)

8. 1.2 Mesoscale vs. synoptic scale Storm Predictions Center Meso-analysis page Fig. 1.3

9. 1.2 Mesoscale vs. synoptic scale 1.2.1 gradient wind balance 1.2.2 hydrostatic balance on chalkboard Fig. 1.4