## Geophysical Fluid Dynamics

Office: Burnside Hall 910

Tel.: (514) 398-8075

Fax.: (514) 398-6115

bartello [at] meteo.mcgill.ca (E-mail)

## Research interests

My research employs both theoretical and numerical techniques to study fluid turbulence in the atmosphere and oceans. A major recent thrust has been the study of the statistical nature of the flow as a function of rotation and stratification. The simplifying assumptions employed at larger scales, that rotation and stratification terms in the governing equations are predominant and approximately balanced by other terms, become invalid at smaller scales. The interactions between large-scale vortices and more general turbulent and wave motions are therefore the subject of these studies, as is the effect on the turbulent transport of passive scalars such as pollutants or ozone. A simple example is whether turbulent motions preferentially send energy downscale (as in a breaking wave at the shore) or upscale (as in the merging of two eddies to make a larger one). Both are known to occur, depending on the relative strengths of rotation and stratification. Both must be accounted ! for in coarse-resolution models, such as the ones used for weather and climate studies, but clearly in a different way.

In the large-scale limit wave motion is dissipated via downscale transfer to molecular scales. In this environment attention is naturally directed to the vortices, as they dominate the flow. They have often been considered as isolated, both from each other and from the rest of the motion. However, a recent examination of large-scale turbulence without waves (2D turbulence) was able to formalize the separation between isolated eddies and a low-level background of vorticity filaments. It remains to be seen whether these results extend to more complete models of geophysical flows.

Since there is a reliance on numerical simulation, research on the numerics is undertaken in parallel. At the expense of accuracy, weather and climate models are forced to use numerical methods that allow for an enormous reduction in the true range of time and length scales. Minimizing the numerical damage as a function of flow statistics is another research priority.

I am also involved with the Applied Math group in the Department of Mathematics and Statistics as well as the McGill seminar series in Computational Science and Engineering.

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## Some recent publications

Sisi Chen, Peter Bartello, MK Yau, PA Vaillancourt, Kevin Zwijsen, Cloud Droplet Collisions in Turbulent Environment: Collision Statistics and Parameterization, Journal of the Atmospheric Sciences, 73, 621-636.

Olivier Asselin, Peter Bartello, David N Straub, On quasigeostrophic dynamics near the tropopause, Physics of Fluids, 28, 026601.

Hossein A Kafiabad, Peter Bartello, Balance dynamics in rotating stratified turbulence, Journal of Fluid Mechanics, 795, 914-949.

Hossein Amini Kafiabad, Peter Bartello, Rotating stratified turbulence and the slow manifold, Computers & Fluids, in press but online. (This was an invited (but strictly refereed) contribution to a special issue dedicated to the work of CE Leith.)

Kafiabad, H. and Bartello, P., 2016, Balance dynamics in rotating stratified turbulence, J. Fluid Mech. in press.

Asselin, O., Bartello, P. and Straub, D.N., 2016, On quasigeostrophic dynamics near the tropopause, Phys. Fluids 28, 026601

Chen, S., Bartello, P., Yau, M.-K., Vaillancourt, P. and Zwijsen, K., 2016, Cloud droplet collisions in a turbulent environment: Collision statistics and parameterization, J. Atmos. Sci. 73, 621-636.

Bartello, P. and S.M. Tobias, 2013, Sensitivity of stratified turbulence to the buoyancy Reynolds number, J. Fluid Mech. 725, 1-22.

Devenish, B.J., P. Bartello, J.-L. Brenguier, L.R. Collins, W.W. Grabowski, R.H.A. IJzermans, S.P. Malinowski, M.W. Reeks, J.C. Vassilicos and Z. Warhaft, 2012, Droplet growth in warm turbulent clouds, Q. J. Roy. Met. Soc. 138, 1401-1429.

Bartello, P., 2010: Quasigeostrophic and stratified turbulence in the atmosphere. In "Turbulence in the Atmosphere and Oceans", D.G. Dritschel editor. Springer.

Bartello, P., B.J. Devenish, J.D. Haigh, and J.C. Vassilicos, 2010, Clouds and Turbulence, Bull. Amer. Meteor. Soc. 91, 1087-1089.

Ngan, K., P. Bartello and D.N. Straub, 2009: Predictability of Rotating Stratified Turbulence, J. Atmos. Sci. 66, 1384-1400

Sacher, W. and P. Bartello, 2008: Sampling errors in ensemble Kalman filtering. Part II Application to a barotropic model, Mon. Wea. Rev. 137. 1640-1655.

Sacher, W. and P. Bartello, 2008: Sampling errors in ensemble Kalman filtering. Part I Theory, Mon. Wea. Rev. 136, 3035-3049

Spyksma, K. and P. Bartello, 2008: Small-scale moist turbulence in numerically-generated convective clouds, J. Atmos. Sci. 65, 1967-1978.

Ngan, K., P. Bartello and D.N. Straub, 2008: Dissipation of synoptic-scale flow by small-scale turbulence, J. Atmos. Sci. 65, 766-791.

Spyksma, K. and P. Bartello, 2008: Predictability in wet and dry convective turbulence, J. Atmos. Sci. 65, 220-234.

Bourouiba, L. and P. Bartello, 2007: The intermediate Rossby number range and 2D-3D transfers in decaying rotating homogeneous turbulence, J. Fluid. Mech. 587, 139-161.

Waite, M.L. and P. Bartello, 2006: The transition from geostrophic to stratified turbulence, J. Fluid Mech. 568, 89-108.

Spyksma, K., P. Bartello, and M.K. Yau, 2006: A Boussinesq moist turbulence model. J. Turbulence, 7 (32), 1-24. DOI: 10.1080/14685240600577865.

Charron, M., P.L. Houtekamer and P. Bartello, 2006: Assimilating Synthetic Radar Data at the Mesoscale with an Ensemble Kalman Filter: A Perfect Model Experiment, Mon. Wea. Rev. 134, 618-637.

Waite, M.L. and P. Bartello, 2006: Stratified turbulence generated by internal gravity waves, J. Fluid Mech. 546, 313-339.

Franklin, C.N., P. Vaillancourt, M.-K. Yau and P. Bartello, 2005: Collision rates of Cloud Droplets in Turbulent Flow, J. Atmos. Sci. 62, 2451-2466.

Ngan, K., D.N. Straub, and P. Bartello, 2005: Aspect ratio effects in quasi-2D turbulence, Phys. Fluids, 17, 125102.

Ngan, K., D.N. Straub and P. Bartello, 2004: Three-dimensionalisation of freely-decaying two-dimensional flows, Phys. Fluids, 16, 2918-2932.

Waite, M.L. and P. Bartello, 2004: Stratified turbulence dominated by vortical motion, J. Fluid Mech. 517, 281-308.

Vaillancourt, P.A., M.K. Yau, P. Bartello, and W.W. Grabowski, 2002: Microscopic approach to cloud droplet growth by condensation. Part II: Turbulence, clustering and condensational growth. J. Atmos. Sci., 24, 3421-3435.

Bartello, P., 2002: Two-Dimensional Turbulence, Invited contribution to The Encyclopedia of Atmospheric Sciences (eds. J.R. Holton, J. Pyle and J. A. Curry), Academic Press.

Bartello, P., 2002: A comparison of time discretization schemes for two-timescale problems in geophysical fluid dynamics, J. Comput. Phys., 179, 268-285.

Bartello, P., 2000: Using low-resolution winds to deduce fine structure in tracers, Atmos.-Ocean, 38, 303-320.

Bartello, P. 2000: Potential Vorticity, Resonance and Dissipation in Rotating Convective Turbulence, Ch. 14 in Geophysical and Astrophysical Convection (eds. R. H. Kerr, P. Fox and C.-H. Moeng), Gordon and Breech.

Lilly, D.K., G. Bassett, K. Droegemeier and P. Bartello, 1998: Stratified Turbulence in the atmospheric Mesoscales, Theoret. Comput. Fluid Dyn. 11, 139-153.