METR112- Global Climate Change: Urban Climate System Professor Menglin Jin San Jose State University Outline: Urban observations Urban heat island effect Urban aerosol Urban rainfall
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
Why do we need to Study Urban regions? • 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
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 Modelin press by Natural Hazards. Jin, M. and M. J. Shepherd, 2007: Aerosol effects on clouds and rainfall: urban vs. ocean. Revised for JGR
43% of Land Area Dominated by Agriculture % of Land Area Built-up 3 - 6%
43% of Land Area Dominated by Agriculture % of Land Area Built-up 3 - 6%
1. Satellite remote sensing on urban regions MODIS land cover Red color means urban built-up
pictures made by U.S. Defense Meteorological Satellites Program (DMSP)
The Afternoon Satellites“A-Train” of Earth Observing System (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? MLS HIRDLS TES OMI
Satellite measurements show unique features of • Urban Surface Land cover – urbanization coverage Surface Temperature – Urban Heat Island Effect Vegetation coverage Emissivity Albedo • Atmosphere Clouds Rainfall Aerosol
Satellite observations retrieve urban system: Land surface properties: surface temperature, surface albedo, emissivity, soil moisture, vegetation cover Atmosphere conditions: aerosol, clouds, and rainfall It shows that urbanization significantly changes weather and climate
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
Surface temperature Urban Heat Island Effect (UHI): Urban surface is hotter than that of surrounding non-urban regions We need to understand why and what are UHI effects
Urbanization Effects Land Surface Energy Budget: (1-α)Sd +LWd-εσTskin4 +SH+LE + G= 0 Dr. Menglin Jin San Jose State University
Urbanization impacts on skin temperature 10°C !!! 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.
50km Local Urbanization changes surface temperature Urban heat island effect Daytime MODIS Nighttime 50km 50km
MODIS Observed Global urban heat island effect Jin et al. 2005 J. of Climate
Comparison of skin temperature for 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 surface Surface 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 Turbulence production Radiation attenuation Canopy heating & cooling Radiation trapping Urban thermal properties e.g., CLM: (NCAR, DAO) NOAH: (NCEP)
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: (1-α)Sd +LWd-εσTskin4 +SH+LE + G= 0 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
NASA MODIS observed Aerosol Distribution July 2005
Urban Pollution Sources Aerosols are solid/liquid particles pending in atmosphere Traffic Size -0.01-100μm Residence time – hours-days Industry Indoor warming
0oC Cloud drop Rain drop Ice crystal Ice precipitation Indirect Effect: serve as CCN Aerosol Direct Effect: Scattering Absorb surface Black carbon heats atmosphere and surface Most aerosols cool surface More aerosol ->small cloud effective radius-> high cloud albedo->cooling (Kaufmann and Koren 2006) More aerosol->reduce rainfall (Rosenfeld 2000)
surface Aerosol Dynamic Effect: Reduce Wind and Precipitation wind “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)
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!
Aerosol decreases surface insolation Total solar radiation decreased by aerosol=20Wm-2 Based on NASA GMAO radiative transfer model (Jin, Shepherd, and King, 2005, JGR)
6-year averaged AERONET measurements Beijing New York City • 6-year daily averaged aerosol optical thickness (AOT) show • significant differences between Beijing and New York City • seasonal variation of urban aerosol
MM5-Urban Model Study: Extreme case (Solar radiation reduced by -100wm-2) Beijing 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.
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)
Professor Marshall Shepherd of The University of Georgia found: Human Activities In Arid Urban Environments Can Affect Rainfall And Water Cycle http://www.sciencedaily.com/releases/2006/06/060619222554.htm 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.