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Results of the Town Energy Budget (TEB) coupled to the Regional Atmospheric Modeling System (RAMS) over Washington DC
15 January 2009
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Overview
Motivation and Effort
Models and Data
Model set up
Results
Summary and Conclusions
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Motivation
UHI Effect is a well established phenomenon
Impacts sensible weather (e.g. PBL) of urban area
Studies have shown that the UHI can even interact/alter local mesoscale flow regimes
Motivated the creation of parameterizations in models; however, studies done at high (<2km) resolution
Current operational models use grid resolutions of km, thus capturing mesoscale flow regimes
Primary tool used for sensible weather forecasts
Using land surface models not designed to model UHI
PBL’s over urban areas likely not well represented
Mesoscale flow interactions not possible
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Motivation
Studies have shown Air quality, dispersion, and military TDA’s are sensitive to PBL parameters
Used heavily in urban areas
Often driven by operational meteorological NWP
In addition, in 2000 nearly 50% of the world population is urban and expected to grow significantly in years to come (Cohen,2003):
Thus any environmental impact of UHI will be felt by a disproportionate part of the population
Result: Current operational forecasts in/around urban centers not accounting for UHI effects
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This Effort
Primary question of my work: Can an urban parameterization improve simulation of a PBL over an urban area (Wash DC) using an typical ‘operational’ model set-up (e.g. 4-12km, fewer vertical layers)
Secondary Questions (not addressed in this talk):
What are the primary sensitivities of the coupled system with an eye towards issues to ‘operationalization’
How detailed does morphology information need to be?
How detailed does land surface information need to be?
Are the differences between the simulated PBL’s significant to follow-on applications (e.g. dispersion, military TDA’s)
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This Effort
Used RAMS V4.3 coupled to LEAF-2 Land Surface Model with a ‘typical’ operational setup
Urban Parameterization: Town Energy Balance (TEB) Model, Masson (2000)
Well documented/validated ‘medium’ complexity parameterization
Completed Rozoff (2003) coupling to LEAF-2
Created a 1km morphology database
Description
Option
Grid Structure
Arakawa C Grid; 3 fixed nested (80, 20, 5 km)
PBL Parameterization
Mellor-Yamada
Radiation Parameterization
Chen, both LW and SW
Lower Boundary
LEAF-2 with Town Energy Balance
Lateral Boundary
Klemp/Wilhelmson
Level of First Model Layer
23 Meters (11m for those written to center)
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Models and Data
Performed modeling over Washington DC for three days in 1984
1984 was chosen due to a year long field campaign called the Metropolitan Tracer Experiment (METREX) that provided additional sources of met data
Present work from 26 Jun 1984 a warm summer day/night with SSW flow on the back side of departing high pressure
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Models and Data
Meteorology data was available for a few sites around DC
Importance was placed on obtaining both surface and elevated data
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Subjective Results
What did the addition of TEB do to the simulation and how does it compare with what we would anticipate?
26 Jun 84:
26 Jun: 2200L Temperature (C) TEB – No TEB
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Subjective Results
26 Jun 84:
26 Jun: 1300L Wind Speed (m/s) TEB – No TEB
27 Jun: 0000L Wind Speed (m/s) TEB – No TEB
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Subjective Results
26 Jun 84:
26 Jun: 2200L PBL Height TEB – No TEB
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Subjective Results
26 Jun 84:
26 Jun: 2200L Streamlines No -TEB
26 Jun: 2200L Streamlines TEB
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Objective Results
What did the addition of TEB do to the simulation and how does it compare with what was measured?
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Objective Results
What did the addition of TEB do to the simulation and how does it compare with what was measured?
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Objective Results
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Objective Results
What did the addition of TEB do to the simulation and how does it compare with what was measured?
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Objective Results
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Objective Results
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Conclusions
The addition of TEB allowed the model to simulate many features common to a UHI and therefore seems to be working ‘properly’
Comparisons against observational data suggests:
TEB is moving the simulation of the PBL closer to observations within the core of the urban environment
Both models struggle with observations near the urban transition with TEB is likely over doing things somewhat
possibly due to land surface representation at 5km grid spacing
Argue that overall TEB is moving the PBL in a better direction
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BACKUPS
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Motivation
These facts have driven the research community to develop a number of urban parameterizations designed for use with NWP models
Designed to supplement a parent LSM in urban areas
Vary in sophistication from simple ‘bulk’ approaches to fully coupled and integrated land and atmospheric parameterizations
Almost all application work done with urban parameterizations in peer reviewed literature has been done with very fine resolution modeling (<2km)
Also often initialized with operational NWP
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Land Surface Model
Each class of land surface is given different characteristics such as albedo, surface roughness, displacement height, thermal properties etc
Urban is generally treated as vegetation
No capacity for 3D geometry effects
No ability to add anthropogenic sources
Thermal characteristics poorly represented
Result: LSM not designed to produce a UHI or any of its impacts
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Models and Data
Urban Parameterization: Town Energy Balance (TEB) Model, Masson (2000)
Treats the urban area as a 3D volume with each grid cell containing a local street canyon system of roofs, walls, and roads
Models three different energy balances (road, roof, wall)
Utilizes a user provided set of morphology characteristics that describe the urban landscape to perform its calculations
All fluxes calculated in this 3D volume are provided as surface inputs to the parent model, even if the actual morphology of the urban area extends into the lower layers of the model
Allows for anthropogenic fluxes both direct and indirect
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Models and Data
Mesoscale Model: RAMS 4.3 – Fully non-hydrostatic mesoscale model with an extensive history of atmospheric simulation from 200m to 2000km
Land Surface Model: Land Ecosystem-Atmospheric Feedback-2 (LEAF-2)
Fully coupled to RAMS
Utilizes 18 Biosphere-Atmosphere Transfer Scheme (BATS) vegetation classes
Another 12 classes were defined from the NASA/NOAA Land Data Assimilation System (LDAS)
LEAF-2 offers the capability to model multiple land patches per grid cell
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Models and Data
TEB requires the following Morphology related data (all are grid cell averages):
Average bld height
Fractional area of bld
Building Aspect Ratio
Dynamic Roughness
Albedo/Emis Roads
Albedo/Emis Roofs
Albedo/Emis Walls
Number of layers roofs/roads/walls
Thickness of layers
Thermal cond of layers
Heat capacity of layers
Internal Temp Bld
SH/LE traffic
SH/LE Industry
For this work I created a 1km morphology dataset that allowed me to vary variables in red
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Models and Data
Morphology data over Washington DC supplied by my efforts and allowed to vary by gridcell… all other locations were given a default set of fixed morphology
Three different sets of land surface data sets were obtained for sensitivity testing
Standard 30s (1km) AVHRR dataset provided with RAMS
A Land Class/Land Use (LULC) 30m dataset
LULC modified with Morphology vegetation estimates
Designed to estimate the actual non-natural land cover
AVHRR: 72% LULC: 60% LULC-Mod: 37%
LULC-Mod was the primary dataset
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Models and Data
Description
Option
Grid Structure
Arakawa C Grid; 3 fixed nested (80, 20, 5 km)
PBL Parameterization
Mellor-Yamada
Radiation Parameterization
Chen, both LW and SW
Lower Boundary
LEAF-2 with Town Energy Balance
Lateral Boundary
Klemp/Wilhelmson
Level of First Model Layer
23 Meters (11m for those written to center)
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Models and Data
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Subjective Results
26 Jun 84:
26 Jun: 2200L Streamlines TEB – No TEB
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Subjective Results
26 Jun 84:
27 Jun: 1000L Temperature (C) TEB – No TEB
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Objective Results
Takoma Tower 60m Winds: Averaged L Obs: 2m/s No TEB: 4.0 m/s TEB: 3 m/s
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Objective Results?
26 Jun 84:
26 Jun: 2200L Streamlines TEB
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