Dr. Keith NGAN

Ph.D. in Physics , The University of Toronto

Assistant Professor (School of Energy and Environment)

Dr. Keith NGAN

Contact Information

Office: AC1-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 Duan & K Ngan, 2016:  Effects of time-dependent inflow perturbations on turbulent flow in a street canyon, in preparation.
  • K Ngan & KW Lo, 2016: Linear error dynamics for turbulent flow in urban street canyons, Journal of Applied Meteorology and Climatology, submitted.
  • KW Lo & K Ngan, 2016: Characterising urban ventilation and exposure using Lagrangian particles, Journal of Applied Meteorology and Climatology, submitted.
  • KW Lo, K Ngan, WK Chiu, G. Duan, 2016: Towards exposure-based health impact indicators: application to Hong Kong, Public Administration and Policy, submitted.
  • 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

  • "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)
  • Effects of time-dependent perturbations on urban flow and dispersion
  • Vortex dynamics in urban domains

Positions available

  1. A postdoctoral fellow/research associate is sought for the RGC project, Air Pollution in Elevated Walkway Microenvironments in Urban Street Canyons (PI: Prof. Peter Brimblecombe, SEE). The successful candidate will perform numerical simulations of flow and dispersion around several elevated walkways in Hong Kong. The aim is to describe the influence of the walkway structure on pollutant concentrations inside and outside the walkway. Experience with computational fluid dynamics is essential. A PhD or MSc in mechanical engineering, civil engineering or a related field is required. The initial appointment will be for 12 months (with the possibility of reappointment). The position is available immediately.

  2. Research opportunities are available for undergraduate students with interests in computational fluid dynamics urban air quality.

Research group

Current members

  • Postdoctoral fellows

    • Gantuya Ganbat (PhD Seoul National University), September 2016 - date

    • Ghar Ek Lau (PhD University of New South Wales), September 2016 – date
  • PhD students

    • Guangdong Duan, September 2014 – date
  • Research Assistants

    • K.W. Wong, July 2016 – date
    • J. Chang & Y. Chen, July 2016 – date

Former members

  • Postdoctoral fellows
    • James G. Jackson (PhD University College London), April 2015 - date
    • Ka Wai Lo (PhD University of Illinois at Urbana-Champaign), November 2013 – January 2016
  • BEng Final-Year Project Students
    • G. Xu (Now MSc, Columbia University), D. Kong, G. Ma, 2015-16
  • Summer interns

    • T. Ying (2014; currently PhD at University of Edinburgh)