Urban land-surface impacts on atmospheric processes for Indianapolis, Indiana
Open Access
- Author:
- Sarmiento, Daniel Perez
- Graduate Program:
- Meteorology
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- November 28, 2017
- Committee Members:
- Kenneth James Davis, Dissertation Advisor/Co-Advisor
Kenneth James Davis, Committee Chair/Co-Chair
David R Stauffer, Committee Member
Fuqing Zhang, Committee Member
Andrew Mark Carleton, Outside Member - Keywords:
- Land-surface interactions
Urban meteorology
WRF - Abstract:
- As part of the Indianapolis Flux experiment, observational studies were conducted to quantify the land-surface interactions between the urban surface and the atmosphere. Meteorological simulations were also executed to investigate the ability to replicate these interactions in numerical weather models. The simulation of these land-surface interactions is crucial in the simulation of atmospheric processes and meteorological variables. Deficiencies in the model were identified and through the integration of observations, several of these deficiencies were addressed. A set of simulations was performed by implementing different PBL schemes, urban canopy models (UCMs), and a model subroutine was created in order to reduce an inherent model overestimation of urban land cover. It was found that accurately representing the amount of urban cover in the simulations reduced the biases in most cases during the summertime (SUMMER) simulations. The simulations that used the BEP urban canopy model and the Bougeault & Lacarrere (BouLac) PBL scheme had the smallest biases in the wintertime (WINTER) simulations for most meteorological variables, with the exception being wind direction. The model configuration chosen had a larger impact on model errors during the WINTER simulations, whereas the differences between most of the model configurations during the SUMMER simulations were not statistically significant. Satellite-derived observations of land-surface temperature showed that the difference between the city and rural areas of Indianapolis was as high as 10K during the daytime and as high as 6K during the nighttime. The land-surface temperature enhancement was similar to values reported in other cities, such as Seoul, South Korea (8K) and Tokyo, Japan (12K). The urban environment reduced the wind speed by an average of ~3 m s-1 throughout a layer that extended ~100 meters above the land-surface. The boundary layer height over the urban surface was found to be 10% higher than the boundary layer height over the more rural areas surrounding Indianapolis. This boundary layer enhancement was lower than expected given that Indianapolis exhibited other urban enhancements that were more characteristic of larger metropolitan cities. Using the land-surface definition algorithm that was developed and a model configuration that was proven to be optimal, parameterizations and parameter values were changed to better simulate the urban atmospheric enhancements and land-surface processes seen in the observations. As the surface roughness increased, the skill of the model generally improved for most meteorological variables including: 2m air temperature, friction velocity, and 10m wind speed and direction. The only detrimental effect caused by the increase in surface roughness occurred when the sensible heat flux over the city was simulated. This detriment was small when compared to the overall errors because larger issues, such as inaccurate land-surface characterization, overestimation of solar radiation in both cloudy and clear-sky conditions, and the necessity to parameterize many of the atmospheric and surface processes, were a larger contributor to the surface energy flux errors. Allowing the model to ingest observable data in order to create heterogeneous parameter values throughout the model added a layer of flexibility that greatly improved the simulation of urban enhancement processes. Many of the parameterizations in the model can still be improved upon to further reduce the simulated errors of most meteorological variables, especially the variables that define the energy fluxes at the land-surface.