METR112- Global Climate Change:Urban Climate System

Professor Menglin JinSan Jose State University

Outline:

Urban observationsUrban heat island effectUrban aerosolUrban rainfall

SF, 2008

Video: Urban Rainfall Effect

http://www.met.sjsu.edu/metr112-videos/MET%20112%20Video%20Library-MP4/urban%20system/

Urban Rainfall Effect.mp4

Video

• Observe urban system effect

http://www.met.sjsu.edu/metr112-videos/MET%20112%20Video%20Library-MP4/urban%20system/

Animation of Atlanta Tornado

•Urban is an extreme case of human-change natural land cover.

•Urban regions has strong pollution, greenhouse emission.

•60% people in USA live in cities

•Urban has unique water and heat cycles what directly affect human life

Why do we need to Study Urban regions?

Related Publications

Jin, M., J. M. Shepherd, M. D. King, 2005: Urban aerosols and their interaction with clouds and rainfall: A case study for New York and Houston. J. Geophysical Research, 110, D10S20, doi:10.1029/2004JD005081.

Jin, M, R. E. Dickinson, and D-L. Zhang, 2005: The footprint of urban areas on global climate as characterized by

MODIS. Journal of Climate, vol. 18, No. 10, pages 1551-1565

Jin, M. and J. M. Shepherd, 2005: On including urban landscape in land surface model – How can satellite data help? Bull. AMS, vol 86, No. 5, 681-689.

Jin, M. J. M. Shepherd, and Christa Peters-Lidard, 2007: Development of A Parameterization For Simulating the Urban Temperature Hazard Using Satellite Observations In Climate Model in press by Natural Hazards.

Jin, M. and M. J. Shepherd, 2007: Aerosol effects on clouds and rainfall: urban vs. ocean. Revised for JGR

% of Land Area Built-up3 - 6%

43% of Land Area Dominated by Agriculture

% of Land Area Built-up3 - 6%

43% of Land Area Dominated by Agriculture

1. Satellite remote sensing on urban regions

MODIS land coverRed color means urban built-up

Night Light of Tokyo

Night Light of Paris

pictures made by U.S. Defense Meteorological Satellites Program (DMSP)

The Afternoon SatellitesThe Afternoon Satellites“A-Train” of Earth Observing System “A-Train” of Earth Observing System

(EOS)(EOS)

The Afternoon constellation consists of 7 U.S. and international Earth Science satellites that fly within approximately 30 minutes of each other to enable coordinated science

The joint measurements provide an unprecedented sensor system for Earth observations Courtesy of M. King

Aura

Launched July 15, 2004 Is the stratospheric ozone layer recovering? What are the processes controlling air quality? How is the Earth’s climate changing?

HIRDLS

TES

MLS

OMI

Satellite measurements show unique features of

Land cover – urbanization coverageSurface Temperature – Urban Heat Island EffectVegetation coverageEmissivityAlbedo

CloudsRainfallAerosol

•Urban Surface

•Atmosphere

Satellite observations retrieve urban system: Land surface properties: surface temperature, surface albedo, emissivity, soil moisture, vegetation cover

Atmosphere conditions: aerosol, clouds, and rainfall

urbanization significantly changes weather and climate

It shows that

Urban Heat Island Effect (UHI)

This phenomenon describes urban and suburban temperatures that are 2 to 10°F (1 to 6°C) hotter than nearby rural areas.

UHI impacts:

Elevated temperatures can impact communities by increasing peak energy demand, air conditioning costs, air pollution levels, and heat-related illness and mortality

High temperature also enhances surface convection, and causes more clouds and rainfall

Urban Heat Island Effect (UHI): Urban surface is hotter than that of surrounding non-urban regions

Surface temperature

We need to understand why and what are UHI effects

Dr. Menglin Jin San Jose State University

(1-α)Sd +LWd-εσTskin4 +SH+LE + G= 0

Urbanization Effects

Land Surface Energy Budget:

EOS MODIS observed monthly mean daytime shows evident urban heat island effect (Copied from Jin et al, 2005a). The red areas show the dense building regions of Beijing.

Urbanization impacts on skin temperature

10°C !!!

50km

Local Urbanization changes surface temperature

Urban heat island effectDaytime Nighttime

50km 50km

MODIS

Jin et al. 2005 J. of Climate

MODIS Observed Global urban heat island effect

Comparison of skin temperaturefor urban and nearby forests

MODIS

Cities have higher Tskin

than forests

Urbanization changes surface albedo (MODIS)

Urban surface albedo has a 4-6% decrease -> more solar radiation will be absorbed at surface\increase surface temperature

Urbanization reduces surface emissivity (MODIS)

(Jin et al. 2005, J. of Climate)

Urban reduces surface emissivity ->Less longwave radiation emitted from surface More heat is kept at surfaceSurface temperature increases

MODIS15_A2 Leaf Area Index (LAI) over Houston regions

Often times, urban regions reduce surface vegetation cover

Existing Coupled Land-Atmosphere Models:Coarse Resolution, Biogeophysics Focus

BARE SOIL: 15%

10%

GRASSLAND:50%

SHRUBS:

NEEDLELEAFTREES: 25%

e.g., CLM: (NCAR, DAO) NOAH: (NCEP)

Turbulence production

Urban thermal properties

Radiation trapping

Radiation attenuation

Canopy heating & cooling

(1-α)Sd +LWd-εσTskin4 +SH+LE + G= 0

Simulate Urbanization to Examine Its Effects

Land Surface Energy Budget:

(1-α)Sd +LWd-εσTskin4 +SH+LE + G= 0

2. How to Simulate Urban?

Urbanization Modifies Surface Energy Budget:

Urban add new physical processes

What Can be Done ?to reduce negative Urban heat island effects?

Education : a key component of many heat island reduction effort

Cool Roofs: Over 90% of the roofs in the United States are dark-colored. These low-reflectance surfaces reach temperatures of 150 to 190°F (66 to 88°C)

Trees and Vegetation

Cool Pavements

Cool Roofs

Cool roof systems with high reflectance and emittance stay up to 70°F (39°C) cooler than traditional materials during peak summer weather.

The Utah Olympic Oval uses cool roof technology.

What Is a "Cool Roof"?

Cool roof materials have two important surface properties: •a high solar reflectance – or albedo

•a high thermal emittance

Solar reflectance is the percentage of solar energy that is reflected by a surface. Thermal emittance is defined as the percentage of energy a material can radiate away after it is absorbed.

3. Urban Aerosols and Their Direct Effects on Clouds, Surface Insolation, and Surface Temperature

Video

• Urban aerosol effect on rainfall

http://www.met.sjsu.edu/metr112-videos/MET%20112%20Video%20Library-MP4/urban%20system/

Summer Precip w-Pollution.mp4

Winter Precip w-Pollution.mp4

July 2005

NASA MODIS observed Aerosol Distribution

Urban Pollution Sources

Traffic

Industry

Indoor warming

Aerosols are solid/liquid particles pending in atmosphere

Size -0.01-100μm

Residence time – hours-days

Indirect Effect: serve as CCN

Cloud dropRain dropIce crystalIce precipitation

Aerosol Direct Effect: Scattering Absorb

0oC

surface

Black carbon heats atmosphere and surfaceMost aerosols cool surface

More aerosol ->small cloud effective radius->high cloud albedo->cooling (Kaufmann and Koren 2006)

More aerosol->reduce rainfall (Rosenfeld 2000)

Aerosol Dynamic Effect: Reduce Wind and Precipitation

surface

“aerosolized particles created from vehicle exhaust and other contaminants can accumulate in the atmosphere and reduce the speed of winds closer to the Earth's surface, which results in less wind power available for wind-turbine electricity and also in reduced precipitation…”

(Jacobson and Kaufmann 2006)

wind

3.2. Remote Sensing of Aerosol Properties

3.2. Remote Sensing of Aerosol Properties

• International satellite sensors enabling remote sensing of tropospheric aerosols– AVHRR, TOMS, ATSR-2, OCTS,

POLDER, SeaWiFS, MISR, MODIS, AATSR, MERIS, GLI, and OMI

Michael King, NASA GSFC

Aerosol-Cloud Relation

AOD vs. water cloud effective radius

More aerosols lead to smaller cloud droplets!

Total solar radiation decreased by aerosol= 20Wm-2

(Jin, Shepherd, and King, 2005, JGR)

Aerosol decreases surface insolation

Based on NASA GMAO radiative transfer model

par AOT

0

0.1

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0.9

0 1 2 3 4 5 6 7

month

Beijing

New York

6-year averaged AERONET measurements

6-year daily averaged aerosol optical thickness (AOT) show •significant differences between Beijing and New York City•seasonal variation of urban aerosol

Beijing

New York City

New York Ftotal

-70

-60

-50

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ch

an

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flu

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12pm

Reduction on surface insolation, New York City

Beijing Ftotal

-160

-140

-120

-100

-80

-60

-40

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0 1 2 3 4 5 6 7

month

ch

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Reduction of surface insolation, Beijing

MM5-Urban Model Study: Extreme case (Solar radiation reduced by -100wm-2)

How cold can the surface become due to the surface insolation decrease, in an urban environment?For Beijing, aerosols cold the surface by more than 5°C in daytime.

Beijing

Urban model simulation over New York City For June 15-16, 2006

For NYC, aerosol colds the surface by 1°C in daytime.

Urban Effects on Climate: An Analogue

Urban Effects on Radiative Forcing Known, but Effects on Water Cycle Processes (e.g. Precipitation Variability) Less Understood (IPCC, 2007)

Human Activities In Arid Urban Environments Can Affect Rainfall And Water Cycle

http://www.sciencedaily.com/releases/2006/06/060619222554.htm

Professor Marshall Shepherd of The University of Georgia found:

a 12-14 percent increase (which scientists call an anomaly) in rainfall in the northeast suburbs of Phoenix from the pre-urban (1895-1949) to post-urban (1950-2003) periods.

A case for Shang Hai, China

ShangHai city

Rural regions

Daytime, monthly skin temperature of Shanghai is higher than surrounding cropland

ShangHai

cropland

Menglin Jin, San Jose State University

UHI

UHI Is observed for nighttime for all months in year

Menglin Jin, San Jose State University

Class participation:

Climate Game!

City A

City B

City C

City D

City E

City F

City G

Climate Game Climate Game NamesNames

Match the city with the corresponding climatology by indicating Match the city with the corresponding climatology by indicating the appropriate letterthe appropriate letter

Sacramento, California (38°°N) _____________Phoenix, Arizona (33°N)Phoenix, Arizona (33°N) __________________________Denver, Colorado (40°N)Denver, Colorado (40°N) __________________________Iquitos, Peru (4°S)Iquitos, Peru (4°S) __________________________Mobile, Alabama (30°°N) _____________Winnipeg, Canada (50°°N) _____________Fairbanks, Alaska (65°°N) _____________