Dr. Keith NGAN

Ph.D. in Physics , The University of Toronto

Assistant Professor (School of Energy and Environment)

Dr. Keith NGAN

Contact Information

Office: YEUNG-B5436
Phone: +(852)-3442-6702
Fax: +(852)-3442-0688
Email: keith.ngan@cityu.edu.hk
Time slots for consultation

Research Interests

  • atmospheric dynamics

  • fluid dynamics

  • numerical weather prediction

  • turbulence

  • urban meteorology

Dr. Keith Ngan obtained his B.Sc. in Physics and Chemistry from the University of British Columbia and his M.Sc. and Ph.D. in Physics from the University of Toronto. Subsequently he was a postdoctoral fellow at the University of Chicago and a research associate at McGill University. In 2008 he moved to the UK Met Office, where he worked as a senior research scientist in the numerical weather prediction division. In 2013 he joined City University of Hong Kong as an Assistant Professor in the School of Energy and Environment.

Dr. Ngan's research seeks to improve understanding of basic dynamical processes in the atmosphere through high-resolution numerical modelling. He is especially interested in interdisciplinary research, more specifically the application of techniques and approaches from applied mathematics and fluid dynamics to practical atmospheric problems. His main areas of expertise are turbulence, data assimilation, atmospheric modelling and scalar mixing and dispersion. The current focus of his research is urban boundary-layer meteorology.

Research Interests:

  • atmospheric dynamics

  • fluid dynamics

  • numerical weather prediction

  • turbulence

  • urban meteorology

Publications

  • G.E Lau & K. Ngan, 2018:  Analysing urban ventilation in building arrays with the age spectrum and mean age of pollutants, Building and Environment, in press, doi:10.1016/j.buildenv.2018.01.010.
  • G. Duan & K. Ngan, 2018: Effects of Time-Dependent Inflow Perturbations on Turbulent Flow in a Street Canyon, Boundary-Layer Meteorology, in press,  doi:10.1007/s10546-017-0327-1
  •  K.W. Lo & K. Ngan, 2017: Characterising urban ventilation and exposure using Lagrangian particles. Journal of Applied Meteorology and Climatology, 56, 1177-1194, doi:10.1175/JAMC-D-16-0168.
  •  K. Ngan & K.W. Lo, 2017: Linear error dynamics for turbulent flow in urban street canyons. Journal of Applied Meteorology and Climatology, 56, 1195-1208, doi:10.1175/JAMC-D-16-0173.1
  •  K. Ngan & K.W. Lo, 2016: Revisiting the flow regimes for urban street canyons using the numerical Green's function, Environmental Fluid Mechanics, 16, 313–334. doi:10.1007/s10652-015-9422-3.
  • KW Lo & K Ngan, 2015: Characterising the pollutant ventilation characteristics of street canyons using the tracer age and age spectrum, Atmospheric Environment, 122, 611-621,  DOI:10.1016/j.atmosenv.2015.10.023
  • K Ngan & KW Lo, 2015: Revisiting the flow regimes for urban street canyons using the numerical Green's function, Environmental Fluid Mechanics, 16, 313-334, DOI:10.1007/s10652-015-9422-3.
  • KW Lo & K Ngan, 2015: Predictability of turbulent flow in street canyons, Boundary-Layer Meteorology, 156, 191-210, DOI:10.1007/s10546-015-0014-z.
  • MJP Cullen & K Ngan, 2013: On the relationship between stratospheric structure and blocking, Philosophical Transactions of the Royal Society A, 371, 2012018, DOI:10.1098/rsta.2012.0180.
  • N.B. Ingleby, A.C. Lorenc, K. Ngan, R. Rawlins & D.R. Jackson, 2012: Improved variational analyses using a nonlinear humidity control variable, Quarterly Journal of the Royal Meteorological Society, 139, 1875-1887, DOI:10.1002/qj.2073.
  • K. Ngan & G.E. Eperon, 2012: Middle atmosphere predictability in a Numerical Weather Prediction Model, Quarterly Journal of the Royal Meteorological Society, 138, 1366-1378, DOI:10.1002/qj.984.
  • K. Ngan & J. Vanneste, 2011: Scalar decay in a three-dimensional chaotic flow, Physical Review E, 83, 056306, DOI:10.1103/PhysRevE.83.056306.
  • K. Ngan, P. Bartello & D.N. Straub, 2009: Predictability of rotating stratified turbulence, Journal of the Atmospheric Sciences, 66, 1384 – 1400, DOI:10.1175/2008JAS2799.1.
  • K. Ngan, P. Bartello & D.N. Straub, 2008: Dissipation of synoptic-scale flow by small- scale turbulence, Journal of the Atmospheric Sciences, 65, 766 – 791, 10.1175/2007JAS2265.1.
  • K. Ngan, D.N. Straub & P. Bartello, 2005: Aspect ratio effects in quasi-two- dimensional turbulence. Physics of Fluids, 17, 125102-1 –125102-17, DOI:10.1063/1.2139685.
  • K. Ngan, D.N. Straub & P. Bartello, 2004: Three-dimensionalization of freely-decaying two-dimensional turbulence. Physics of Fluids, 16, 2918 – 2932, DOI:10.1063/1.1763191.
  • T.G. Shepherd, J.N. Koshyk & K. Ngan, 2000: On the nature of large-scale mixing in the stratosphere and mesosphere. Journal of Geophysical Research, 105, 12,433 – 12,460.
  • K. Ngan & R.T. Pierrehumbert, 2000: Spatially correlated and inhomogeneous random advection. Physics of Fluids, 12, 822 – 834.
  • K. Ngan & T.G. Shepherd, 1999: A closer look at chaotic advection in the stratosphere. Part I. Geometrical Structure. Journal of the Atmospheric Sciences, 56, 4134 – 4153.
  • K. Ngan & T.G. Shepherd, 1999: A closer look at chaotic advection in the stratosphere. Part II. Statistical diagnostics. Journal of the Atmospheric Sciences, 56, 4154 – 4169.
  • K. Ngan & T.G. Shepherd, 1997: Chaotic mixing and transport in Rossby-wave critical layers. Journal of Fluid Mechanics. 334, 315 – 351.
  • K. Ngan & T.G. Shepherd, 1997: Comments on some recent measurements of anomalously steep N2O and O3 tracer spectra in the stratospheric surf zone. Journal of Geophysical Research, 102, 24,001 – 24,004.
  • K. Ngan, S. Meacham & P.J. Morrison, 1996: Elliptical vortices in shear: Hamiltonian moment formulation and Melnikov analysis. Physics of Fluids, 8, 896 – 913.

Recent talks

  • Atmospheric Science Seminar, National Central University, Jhongli, Taiwan, June 2017
  • "Dispersion and ventilation in urban street canyons", School of Mathematics, University of Edinburgh, December 2016.
  • "Atmospheric predictability from global to urban scales", Earth System Science Programme, Chinese University of Hong Kong, November 2016.
  • "Characterising urban ventilation and exposure with Lagrangian diagnostics", Workshop on Photochemical Smog in China, October 2016. 
  • "Some issues in urban-scale NWP", Numerical Weather Prediction Forum, Hong Kong Observatory, March 2016.
  • "Predictability and linear error dynamics of turbulent flow in street canyons", American Met. Society Joint Conference on Air Pollution Meteorology and its Applications, January 2016.

Current projects

  • Ventilation and mixing timescales for urban air quality (Supported by the Research Grants Council of Hong Kong, 2015-2018; with K.K. Hon, Hong Kong Observatory)
  • Regional vs. local contributions to particulate concentrations in street canyons (Supported by the Environment and Conservation Fund and Woo Wheelock Green Fund, 2016-2018; with Prof. P. Brimblecombe and Dr. Z. Ning, SEE/CityU)
  • Applications of wavelets and multiscale modelling to urban canopy parameterisations (Supported by the Research Grants Council of Hong Kong, 2016-2019; with Prof. P. Bartello, McGill University and K.K. Hon, Hong Kong Observatory)
  • Effects of elevated walkways on urban flow and dispersion (Co-I; with Prof. P. Brimblecombe, SEE)
  • Random-walk models of urban pollutant dispersion (with Prof. J. Vanneste, University of Edinburgh)
  • Predicting winds inside deep urban canopies using vortex dynamics (Supported by the  Research Grants Council of Hong Kong, 2018-2020; with K.K. Hon, Hong Kong Observatory)

Positions available

  1. 'Research opportunities are available for undergraduate and  postgraduate students with interests in computational fluid dynamics, urban air quality, mathematical modelling or atmospheric science

Research group

Current members

  • Postdoctoral fellows

    • Guangdong Duan (PhD, City University of Hong Kong)
  • PhD students

    • Huanhuan Wang

Former members

  • Postdoctoral fellows
    • Ghar Ek Lau (PhD, University of New South Wales; 2016 - 2018)
    • Gantuya Ganbat (PhD, Seoul National University; 2016 - 2018)
    • James G. Jackson (PhD University College London), April 2015 - date
    • Ka Wai Lo (PhD University of Illinois at Urbana-Champaign; 2013 – 2016)
  • Research Assistants
    • Jason Y.L. Chu (now at Hong Kong University of Science and Technology)
  • BEng Final-Year Project Students
    • G. Xu (Now MSc, Columbia University)
    • N. Kong (Now MEng, University of Michigan)
  • Summer interns

    • K.W. Wong (currently MSc at École Polytechnique Fédérale de Lausanne)
    • T. Ying (2014; currently PhD at University of Edinburgh)