ATM S 536 - Winter 2006

We will read five classic papers in mesoscale dynamics. The course format will alternate between "lecture" weeks and "paper" weeks. Paper weeks will consist of two lectures per week, with the Friday session devoted to a discussion of the assigned paper. The Monday and Wednesday lectures will provide background material for the paper. The intervening lecture weeks will provide additional background material for understanding the next (or perhaps previous) paper.

Obviously, five papers do not provide a complete overview of mesoscale dynamics. Additional papers are listed under further reading, although such reading will not be required. The lectures will try to round out the presentation and draw in other points of view. I keeping with my own interests and expertise, 60% of the class will be devoted to matters involving airflow over topography.

Weeks 1-2: Mountain waves and momentum transport

Eliassen, A. and E. Palm, 1960: On the transfer of energy in stationary mountain waves. Geofysiske Publikasjoner, 22, 1-23.
Further reading:
- Durran, D.R., 2003: Lee waves and mountain waves. Encyclopedia of Atmospheric Sciences. Holton, J.R., J. Pyle and J.A. Curry eds. Elsevier Science Ltd., pp. 1161-1170.
- Smith, R.B., 1979: The influence of mountains on the atmosphere. Advances in Geophysics, 21, 87-229 [our focus is on pp. 88-120].
Figures
- Internal gravity waves forced by a compact oscillator in a basic state at rest (animations).
- Comparison of evanescent and vertically propagating waves over sinusoidal topography.
- Comparison of linear vertically propagating and trapped waves forced by an isolated mountain.
- Comparison of nonlinear vertically propagating and trapped waves forced by an isolated mountain.
- Cirrus generated by a vertically propagating wave over the Sierra Nevada.
- Vertically propagating wave over the Andes.
- Trapped lee waves in Saharan dust.
- Trapped lee waves over Iceland.
- Three-dimensional trapped waves generated by the South Sandwhich Islands.
- Three-dimensional trapped wave forming a flying saucer.
- Comparison of very idealized and slightly idealized breaking waves.
Movies
- Very extensive trapped waves over Nevada (60 MB mov file).

Weeks 3-4: Downslope winds

Durran, D.R., 1986: Another look at downslope windstorms. Part I: The development of analogs to supercritical flow in an infinitely deep continuously stratified fluid. J. Atmos. Sci., 43, 2527-2543.
Further reading:
- Smith, R.B., 1985: On severe downslope winds. J. Atmos. Sci., 42, 2597-2603.
- Klemp, J.B. and D.K. Lilly, 1975: The dynamics of wave-induced downslope winds. J. Atmos. Sci., 32, 320-339.
- Durran, D.R., 2003: Downslope winds. Encyclopedia of Atmospheric Sciences. Holton, J.R., J. Pyle and J.A. Curry eds. Elsevier Science Ltd., pp. 1161-1170.
Figures
- Surface wind trace near Boulder. Colorado.
- January 11, 1972 aircraft observations near Boulder, Colorado.
- Bora aircraft observations
Interactive
- Waves on a string

Smolarkiewicz, P.K. and R. Rotunno, 1989: Low Froude number flow past three-dimensional obstacles. Part I: Baroclinically generated lee vortices. J. Atmos. Sci., 46, 1154-1164.
Further reading:
- Smith, R.B., 1989: Comment on "Low Froude number flow past three-dimensional obstacles. Part I: Baroclinically generated lee vortices." J. Atmos. Sci., 46, 3611-3613.
- Smolarkiewicz, P.K. and R. Rotunno, 1989: Reply. J. Atmos. Sci., 46, 3614-3617.
- Epifanio, C.C., 2003: Lee Vortices. Encyclopedia of Atmospheric Sciences. Holton, J.R., J. Pyle and J.A. Curry eds. Elsevier Science Ltd., pp. 1150-1160.
- Smith, R.B., 1989: Hydrostatic airflow over mountains. Advances in Geophysics, 21, 87-229 [our focus is on Section 2].
Figures
- Ship waves generated by the South Sandwhich Islands
- Wakes in stratus off Southern California
- Wakes generated by Hawaii and Alejandro Selkirk Islands
- Lee vortices generated by Cheju Island
- Karman vortices shed by flow past a cylinder
- Baroclinic generation and tilting of horizontal vorticity to create lee vortices
- Downstream wake evolution (nondimensional time Ut/a)
- Stretching of vertical vorticity in a jump to strengthen lee vortices (contours are vertical vorticity, vectors are horizontal winds)

Weeks 7-8: Thunderstorms and Squall lines

Rotunno, R., J.B. Klemp and M.L. Weisman, 1988: A theory for strong, long-lived squall lines . J. Atmos. Sci., 45, 463-485.
Further reading:
- Klemp, J., 1987: Dynanics of Tornadic Thunderstorms. Ann. Rev. Fluid Mech., 19, 369-402.
- Thorpe, A. J., M. J. Miller, and M. W. Moncrieff, 1982: Two-dimensional convection in non-constant shear: A model of mid-latitude squall lines. Quart. J. Roy. Meteor. Soc., 108, 739–762.
- Pandya, R.E. and D.R. Durran, 1996: The influence of convectively generated thermal forcing on the mesoscale circulations around squall lines. J. Atmos. Sci., 53, 2924-2951.
Figures (supercell dynamics)
- Out on the dryline
- Schematic hodograph and airflow in supercell
- Development of initial rotation
- Storm splitting
- Vertical momentum budget
- Shear induced pressure perturbation in relation to the updraft core
- Mean hodograph for tornadic storms
- Simulated split storms with different low-level wind shear
- Vertical pressure gradients: straight-line hodograph
- Vertical pressure gradients: clockwise turning hodograph
- Inflow along the gust front as rotation intensifies
- Streamwise vorticity feeding the updraft as rotation intensifies
Figures (thunderstorm morphology)
- Buoyancy and CAPE
- Thermodynamic soundings
- Wind profiles
- Maximum updraft versus time for different wind shears
- Initial updraft strength as a function of CAPE and shear
- Later updraft strength as a function of CAPE and shear
- Comparison of surface vorticity and updraft strength as a function of CAPE and shear
- Downburst at Stapleton Airport, Denver
Figures (squall lines)

Weeks 9-10: Frontogenesis: the nature and role of ageostrophic motions

Mesoscale Dynamics

(still listed as "Storm Dynamics")