On the Improvements of Boundary-Layer Representation for High-Resolution Weather Forecasting in Coastal-Urban Environments – Dr. David Melecio-Vazquez

by mcjonsey

Doctoral Recipient – David Melecio-Vazquez
Doctoral Program – Mechanical Engineering
Doctoral Thesis Adviser – Jorge E. Gonzalez-Cruz



Baccalaureate Aerospace Engineering & Mechanical Engineering Institution Rensselaer Polytechnic Institute

Dr. David Melecio-Vazquez was a NOAA EPP/MSI Earth System Sciences and Remote Sensing Scholar at The City College New York (CCNY) of the City University of New York (CUNY). His thesis focused on the improvements of weather models over coastal urban environments. He used a combination of ground-based remote sensing and in-situ weather stations for ground-truth comparisons of modeled boundary-layer output from the urbanized-Weather Research and Forecasting (WRF) model. Improved modeling performance resulted from collaboration with the Global Systems Laboratory, National Oceanic and Atmospheric Administration (NOAA) Earth Systems Research Lab (ESRL) in Boulder, CO. David earned a Doctor of Philosophy in Mechanical Engineering from The City College of New York. He holds a Dual Bachelor of Science in Aerospace Engineering and Mechanical Engineering from Rensselaer Polytechnic Institute.

Title of Thesis Research

On the improvements of boundary-layer representation for high-resolution weather forecasting in coastal-urban environments

Thesis Abstract As large urban centers around the world become more densely populated, the global conversion from natural to man-made land surfaces will only increase. These land-use changes affect the urban surface energy budget which in turn changes the structure of the planetary boundary layer (PBL) above. With current high-performance computing systems, meteorological and built environment information can be better utilized to quantify the anthropogenic effects of these modifications. Although these systems have improved forecasting near-surface weather conditions, a comprehensive approach to represent urban impacts on the PBL is still limited. Improved PBL representation can lead to better weather and climate forecasts, benefitting human health, risk reduction from extreme weather events, improved management of airport runways, and better planning for renewable energy resources.

In this dissertation, coastal-urban boundary-layers are investigated to provide: (1) a climatology of coastal-urban PBL thermal structure, (2) an evaluation of a PBL scheme newly coupled to a multilayer urban parameterization, and (3) insights for operational weather forecasting. Ground-based remote sensing is thus used to determine PBL structure over high-density New York City for a summer and winter season to provide insights for a modeling effort. The modeling focused on the evaluation of the performance of the Weather Research and Forecasting (WRF) model in the simulation of NYC impacts during a three-day regional heatwave and sea breeze event. The study proposes a new WRF configuration within the US National Weather Service (NWS)-National Ocean and Atmospheric Agency (NOAA) operational numerical weather prediction (NWP) forecast model. The goal is an improved PBL representation at a high resolution of a 1-km grid over coastal cities by a coupling of the state-of-the-art multi-layer Building Environment Parameterization (BEP) and the Building Energy Model (BEM) schemes to three PBL options, including a first-time linkage with the operational Mellor-Yamada-Nakanishi-Niino (MYNN) Eddy Diffusivity and Mass Flux (EDMF) scheme.

Results showed that climatological clear-sky conditions produced a winter and summer shallow above-rooftop daytime superadiabatic layer that persisted into the night, unlike the traditional surface inversion found over non-coastal, non-urban surfaces. Above this shallow layer, a persistent elevated stable region was found. The heat event WRF simulations showed that MYNN-EDMF produces the best performance in comparison to observed surface temperatures and sea-breeze front progression, with the BouLac PBL scheme best for surface wind speed. MYNN-EDMF also was the most accurate in reproducing the rural PBL case study observations, while its urban PBL structures were most like the climatological thermal structures.

Future efforts should utilize a TKE formulation that includes advection to better capture internal boundary layer effects and more precisely evaluate PBL heights. Future efforts should further refine the anthropogenic heat and building drag formulations, which will further reduce WRF urban temperature and wind speed biases, respectively. It is finally recommended that future NYC-area investigations include case-study and climatological observations at optimal locations for observing the interactions between the urban environment and sea-breeze systems.


Major Findings

Using a microwave radiometer at CCNY to look at temperature profiles yielded the visualization of two aspects of the boundary-layer that is rarely captured due to limited use of this instrument in cities. Summer nighttime boundary-layers over New York City show an unexpected super-adiabatic surface boundary layer. The lack of a surface inversion at night (summer and winter) was also observed. These nighttime results were only seen before in helicopter case studies.

Based on a comparison of boundary-layer schemes over NYC, the MYNN-EDMF showed the best performance over the MYJ and BouLac planetary boundary-layer schemes.

The 1km resolution model over NYC was able to produce a reasonable sea-breeze front footprint, especially in its marine air bifurcation around NYC (previously only modeled in a Beijing thunderstorm event).

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