Multi-scale modeling of urban atmospheres is one of the major frontiers of mathematical geosciences. The latest developments in high performance computing technologies represent an opportunity to advance high resolution simulations of urban atmospheric environments. Among the new capabilities required are improved physics based sub-grid parameterizations and one- or two-way nesting to integrate models of disparate scales. Detailed knowledge of fundamental physical processes and novel computational techniques are used to develop multi-scale nested urban systems models to study the response of urban areas to changing climate. A range of scales, from climate to urban microscale in street canyons are incorporated and some urban infrastructure elements, which have typically evaded in geosystems models hitherto, are included. Analyses and simulations of emergent and other possible scenarios, using mathematical and complex multi-scale systems modeling, are conducted for complex geosystems, thus enabling multi-disciplinary studies on how global change impacts sustainability of urban systems. Through multi-disciplinary collaborations, a team of mathematicians and geoscientists from ASU, Univ. of Notre Dame and researchers from NCAR work closely to develop coupled mesoscale/microscale models with vertical and horizontal nesting techniques; explore the up-scale influence of urban processes and develop deterministic and stochastic parameterization schemes to incorporate subgrid-scale urban effects in climate models; and develop fast, scalable and parallelized numerical algorithms and solvers for effective resolution of multiscale physics phenomena in urban atmospheres using high resolution nested mesoscale/microscale simulations. A selected set of development scenarios are studied and emergent properties as well as extreme events are identified from simulation data. These models and analyses are validated through comparison with extensive data bases available from prior field studies. These knowledge enhance our understandings of the physical processes involved in urban environments and help policy makers design a sustainable strategy for urban developments capable of coping with regional and global climate change. |
| Vertically Nested Mesoscale WRF/Microscale Model: Development of Two-Way Vertical and Horizontal Nesting Capabilities |
| We develop a numerical solver for the fully three-dimensional, moist, compressible nonhydrostatic Navier-Stokes equations for real atmospheric conditions (one and two-way nesting) using combined time-split method and operator splitting computational techniques with a stretched, adaptive grid in the vertical and finer grid spacing in critical regions of the atmosphere. For nesting, the lateral and the upper boundary conditions are treated via implicit relaxation scheme applied in buffer zones where all the prognostic microscale fields are relaxed to those obtained from the mesoscale nests. This new computational technique is demonstrated to be robust compared to those based on the conventional relaxation methods. The equations are cast in conservative form as in WRF, with a new pressure gradient formulation in the momentum equations. In this formulation the number of arithmetic operations required for the pressure gradient evaluations in the horizontal momentum equations is reduced by 20% allowing faster integration. High resolution real case simulations using vertically nested mesoscale WRF/microscale model have been successfully conducted and validated during the Terrain Induced Rotor Experiment (T-REX) campaign of field measurements. |
| Up-scale Influence: Parameterization of Urban Effects in Global Climate Models |
| Previous modeling efforts have focused on quantifying the one-way, down-scale, influences of large-scale climate variability and change on regional climate.The common approach is to constrain a mesoscale model with imposed climatological boundary conditions derived from coarse-resolution (grid size L > 100 km) global climate model simulations. The mesoscale processes do not feedback to the large-scale circulation. Simulations using this nested system of models have helped reveal the changes in mesoscale temperature and precipitation induced by large-scale climate change. If our knowledge on down-scale influence is so far incomplete, progress in understanding the up-scale influence is even slower. In state-of-the-art global climate prediction exemplified by the efforts of Intergovernmental Panel on Climate Change (IPCC 2007), the representation of up-scale influence of urbanization on global climate is restricted to the two aspects of emission of greenhouse gas (GHG) and production of aerosols by human activities. In IPCC climate model simulations, the former is merged with other anthropogenic but non-urban contributions into a globally uniform increase in GHG concentration while the latter is parameterized as a prescribed (but time dependent) radiative forcing with a crude geographical distribution, for instance a greater aerosol cooling effect is imposed to the more heavily populated Northern Hemisphere. The impacts of accelerated urban heat island effect and changes in land surface types due to urban expansion and development have not been incorporated into IPCC's prediction for future global climate. Our study aims at advancing our understanding on the two-way interaction by focusing on the up-scale influences through numerical experiments. |
| Parameterization of diabatic heating and mechanical dissipation |
| Diabatic heating in urban heat island and mechanical dissipation assoicated with different land use are two emergent quantities that need to be parameterized in urban climate models. To incorporate the subgrid-scale heterogeneous surface conditions into the parameterization scheme, we may draw an analogy from the existing treatment for unresolved land-sea contrast within a grid box. In large-scale atmospheric models, a grid box located on the coastline may straddle both land and ocean. In some current climate models, e.g., the Geophysical Fluid Dynamics Laboratory (GFDL) model, the fraction of area covered by sea for each grid box is taken into account to adjust evaporation and other relevant processes for the box. This approach can be adopted for the representation of urban heat island effect on a large-scale grid box in a climate model. When an urban landscape is explicitly resolved, the area covered by roads and built structures should be hotter than that covered by bare soil and vegetation, the latter resemble natural surfaces. Therefore, an enhanced solar radiative heating for the large-scale grid box can be represented. The same strategy for parameterizing diabatic heating may also be adopted for mechanical damping. The unresolved heterogeneous urban landscape, especially the ubiquitous presence of man-made structures, implies a likely overall increase in surface roughness. Its net effect on the large-scale flow may be parameterized as an extra damping in the horizontal momentum equation. Urban processes also affect the variance of these large-scale variables.Recent studies show that spatially correlated stochastic forcing increases the variance of the predicted flow fields to a level that is closer to observation. We employ the same strategy in the stochastic parameterization yet spatialtemporal structure is provided from realistic mesoscale data with high hyterogeneity. |
| Implementation of parameterization schemes and climate model experiments |
| The parameterization schemes developed in house are implemented in a global model to test its effect on large-scale circulation. The parameterized diabatic heating, momentum forcing/dissipation, and stochastic perturbation that represent the effects of unresolved urban processes are imposed to selected grid boxes that individually encompass one or more major metropolitan areas. By tuning the parameterized urban forcing and extracting its effect on large-scale climate from the numerical experiments, we can attempt to address the following basic questions:
|
| High Resolution Numerical Simulations and Analysis of Extreme Events in Urban Atmosphere |
| Studies of how human activities are changing climate predictions show that both sudden and extended weather extremes will be more likely and more variable across the globe. Environmental risks are also increasing because of the changing nature of the environment, both locally and globally. In many critical regions the local environment is already changing faster than it is globally, leading to heat islands in urban areas, flooding and anomalous warming in the Polar Regions and local loss of biodiversity. When hazards are exacerbated by a changing climate, a combination of sustainable policies is necessary. Depending on the particular environment, real-time forecast for imminent hazards are a practical possibility over limited periods, from minutes up to a few months. Analyses and high resolution numerical simulations of emergent and other possible scenarios can test and propose strategies for resilience and sustainability in urban environments. Although the methods used are increasing in reliability, significant uncertainties remain in the underpinning science and in the data. In this regard, high resolution numerical simulations of extreme events in urban atmospheres using coupled mesoscale/microscale models can test and propose strategies and provide new insights for public discussions and decision making with regard to integrated policies for environmental resilience and sustainability in urban environments. |
| Refereed Journal Publications |
| 21. | M Georgescu, A Mahalov, M Moustaoui, "Seasonal hydroclimatic impacts of Sun Corridor expansion", Environmental Research Letters, 2012, 7, 3, 034026 |
| 20. | Fernando, Mammarella, Grandoni et al. "Forecasting PM10 in metropolitan areas: efficacy of neural networks," Environmental Pollution, v.163, 2012, p. 62. |
| 19. | Georgescu; Moustaoui; Mahalov; Dudhia. "Summertime climate impacts of projected megapolitan expansion in Arizona," Nature Climate Change, 2012. |
| 18. | Tang, Knutson, Mahalov, Dimitrova. "The geometry of inertial particle mixing in urban flows, from deterministic and random displacement models," Physics of Fluids, v.24, 2012, p. 063302. |
| 17. | A. Sharma and H.P. Huang. "Regional climate simulation for Arizona: the impact of resolution on precipitation," Advances in Meteorology, 2012. |
| 16. | Dimitrova, Fernando et al. "Relationship between particulate matter and childhood asthma - basis of a future warning system for Central Phoenix," Atmopsheric Chemistry and Physics, v.12, 2012, p. 2479. |
| 15. | Georgescu, M.; Moustaoui, M.; Mahalov, A. and Dudhia, J., "An alternative explanation of the semi-arid urban area 'oasis effect'", J. Geophys. Res.,v.116, 2011, p. 24113 |
| 14. | Baklanov, AA; Grisogono, B; Bornstein, R; Mahrt, L; Zilitinkevich, SS; Taylor, P; Larsen, SE; Rotach, MW; Fernando, HJS. "The Nature, Theory, and Modeling of Atmospheric Planetary Boundary Layers," BULLETIN OF THE AMERICAN METEOROLOGICAL SOCIETY, v.92, 2011, p. 123-128. |
| 13. | Tang, W.; Haller, G. and Chan, PW. "Lagrangian Coherent Structure analysis of terminal winds detected by LIDAR. Part II: structure evolution and flight data analyses," JOURNAL OF APPLIED METEOROLOGY AND CLIMATOLOGY, 50, 2011, 2167-2183. |
| 12. | Tang, W; Chan, PW and Haller, G. "Lagrangian Coherent Structure Analysis of Terminal Winds Detected by Lidar. Part I: Turbulence Structures," JOURNAL OF APPLIED METEOROLOGY AND CLIMATOLOGY, v.50, 2011, p. 325-338. |
| 11. | Mahalov, A; Moustaoui, M and Grubisic, V. "A numerical study of mountain waves in the upper troposphere and lower stratosphere," ATMOSPHERIC CHEMISTRY AND PHYSICS, v.11, 2011, p. 5123-5139. |
| 10. | Georgescu, M; Lobell, DB and Field, CB. "Direct climate effects of perennial bioenergy crops in the United States," PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA, v.108, 2011, p. 4307-4312. |
| 9. | Zajic, D; Fernando, HJS; Calhoun, R; Princevac, M; Brown, MJ and Pardyjak, ER. "Flow and Turbulence in an Urban Canyon," JOURNAL OF APPLIED METEOROLOGY AND CLIMATOLOGY, v.50, 2011, p. 203-223. |
| 8. | Lehner, T.; Waleed, M.; Mahalov A. and J. Leorat. "Mode Coupling Analysis and Differential Rotation in a Flow Driven by a Precessing Cylindrical Container," Geophysical and Astrophysical Fluid Dynamics, v.104, 2010, p. 369-401. |
| 7. | Moustaoui, M; Mahalov, A; Teitelbaum, H; Grubisic, V. "Nonlinear modulation of O-3 and CO induced by mountain waves in the upper troposphere and lower stratosphere during terrain-induced rotor experiment," JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES, v.115, 2010. |
| 6. | Georgescu, M; Lobell, DB. "Perennial Questions of Hydrology and Climate," SCIENCE, v.330, 2010, p. 33-33. |
| 5. | Tang, W; Taylor, JE; Mahalov, A. "Lagrangian dynamics in stochastic inertia-gravity waves," PHYSICS OF FLUIDS, v.22, 2010. |
| 4. | Fernando, HJS; Zajic, D; Di Sabatino, S; Dimitrova, R; Hedquist, B; Dallman, A. "Flow, turbulence, and pollutant dispersion in urban atmospheres," PHYSICS OF FLUIDS, v.22, 2010. |
| 3. | Fernando, HJS; Weil, JC. "WHITHER THE STABLE BOUNDARY LAYER? A Shift in the Research Agenda," BULLETIN OF THE AMERICAN METEOROLOGICAL SOCIETY, v.91, 2010, p. 1475-1484. |
| 2. | Fernando, H.J.S., Zajic, D., Di Sabatino, S., Dimitrova, R., Hedquist, B., and Dallman, A. "Flow, Turbulence and Pollutant Dispersion in Urban Atmospheres," Physics of Fluids,, v.22, 2010, p. 051301-19. |
| 1. | Y. Giga, A. Mahalov and T. Yoneda. "On a Bound for Amplitudes of Navier-Stokes Flow with Almost Periodic Initial Data," Journal of Mathematical Fluid Mechanics, 2010. |
Last Update: 06/12/2013
