2003 EARTH SCIENCE VIDEOTAPES |
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Tape Title | Record ID | Date Produced | TRT: |
Synopsis |
| URBANIZATION AND CLIMATE: HOW CITIES IMPACT GLOBAL CHANGE (AGU 2003)
| G03-067 | 12/08/03 | 00:11:42 | Satellites help scientists observe major urban areas and their environments around the world, as urbanization can impact processes related to clouds, rainfall, air quality, temperature, and climate. For example, urban "heat islands" may alter rainfall patterns during the warm season, increasing rainfall over and downwind of cities. Pollution combined with urban heat retention intensifies thunderclouds, increasing summer precipitation. Coastal cities, with large reservoirs of warm moist air nearby, may experience exaggerated effects. Recent evidence suggests that pollution from cars and factories lessens rainfall downwind of coastal cities in winter by stunting precipitation growth in clouds.
Urbanization may also impact global temperature records, cloud cover, and surface water run-off processes. Recent and future satellites rounding out the NASA's Earth Observing System will provide an unprecedented capability to measure and link components of urban environments that may signify global change in weather, climate, water resources, air quality, or land use.
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TAPE CONTENTS: |
| ITEM (1): Pollution Increases Summer Precipitation - In summer, weaker winds move the clouds more slowly. Heat absorbed by the city and pollution's interference with raindrop formation interact to cause the clouds to intensify before producing precipitation. The onset of rainfall from a cloud leads eventually to its demise by cooling off the air near the ground. The air pollution delays the onset of precipitation, so that the intense storm clouds can build higher and larger before they start precipitating and subsequently dissipating. Therefore, these larger and more intense thunderstorm clouds produce eventually heavier rainfall on the city and the downwind areas. First is the unpolluted, then the polluted case.
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| ITEM (2): Urban Rainfall Effect in Coastal Cities - Cities tend to be 1-10 degrees Fahrenheit warmer than surrounding areas. The added heat destabilizes and changes air circulation around cities. During the warmer months, the added heat creates wind circulations and rising air that produces new clouds or enhances existing ones. Under the right conditions, these clouds evolve into rain-producers or storms. Scientists suspect that converging air due to city surfaces of varying heights, like buildings, also promotes rising air needed to produce clouds and rainfall.
Courtesy: NASA
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| ITEM (3): Pollution Reduces Winter Precipitation - In winter, moist air flows off the ocean and rises over the hills downwind of a coastal city, dropping its rain and snow mainly as it ascends the hills. As pollution from the city is pushed into the clouds by the hills downwind of the city, it interferes with droplet formation in the clouds and makes them smaller, as observed by NASA's satellites. The smaller cloud droplets convert more slowly into precipitation. Instead of precipitating, much of the water in the clouds evaporates, reducing the net rainfall downwind of the urban area by up to 15% to 25% on a seasonal basis. First is the unpolluted, then the polluted case.
Courtesy: NASA
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| ITEM (4): Pollution Inhibits Precipitation Formation - Normal rainfall droplet creation involves water vapor condensing on particles in clouds. The droplets eventually coalesce together to form drops large enough to fall to Earth. However, as more and more pollution particles (aerosols) enter a rain cloud, the same amount of water becomes spread out. These smaller water droplets float with the air and are prevented from coalescing and growing large enough for a raindrop. Thus, the cloud yields less rainfall over the course of its lifetime compared to a clean (non-polluted) cloud of the same size. The split screen compares a normal rain producing cloud (left) with the lack of rain produced from a cloud full of aerosols from pollution.
Courtesy: NASA
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| ITEM (5): Urban Rainfall Shadows - Using the world's first space-based rain radar, scientists found that mean summer-monthly rainfall rates within 35 miles downwind of cities were, on average about 28% greater than the upwind region (regions shown in blue). In some cities, the downwind area exhibited increases as high as 51%. The images depict the urban rain effect east of the I-35 corridor near Dallas, Texas (first image) and near the Atlanta/Birmingham region (second image).
Courtesy: NASA
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| ITEM (6): Urban Heat Islands - Using a specially-outfitted Learjet, NASA researchers collected thermal data about the Atlanta metro area, aligning aircraft data from May 11-12, 1997 with a Landsat 5 satellite image. The "natural" color transitions to daytime temperatures (white hottest, red lower, blue lowest). Daytime air temperatures reached only 80 degrees Fahrenheit, but surface temperatures rose to 118. Buildings cast shadows across pavement and walls of surrounding structures, cooling small areas. The data fades to a nighttime reading with the same colors - heat remains locked in the developed areas; air temperatures cooled to 50 degrees, but surfaces stayed near 75. (G00-015)
Courtesy: NASA
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| ITEM (7): Urban Heat Island - Cloud Formation - This animation shows the outlines of Atlanta and Hartsfield Airport; the tiny dot in the lower left corner of town is the downtown skyline. Observed by a Geostationary Operational Environmental Satellite (GOES), clouds form over the city and pick up strength and size as they develop, moving east. As the city holds onto heat at night, the heat sink creates a low-pressure system, with hot air rising and cooler surrounding air rushing in to replace it and warm up in turn. That heated air condenses and forms thunderclouds. Evidence suggests the phenomenon may be more intense over heavily urbanized areas than in undeveloped places. Red shows the heaviest concentration of precipitation with thick, high clouds; green shows less intense storm areas, and white shows dense surrounding clouds. (G00-015)
Courtesy: NASA
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| ITEM (8): Urban Growth Fuels Heat Islands - In the past 17 years, urban growth in Atlanta has spread and blossomed. Large patches of cropland gave way to commercial and residential developments, and industrialization along some of the main roadways has dramatically altered the face of Georgia's largest city. In this visualization, red and orange points indicate areas of highest urban growth. Researchers assembled data from Landsat satellites in the early 70''s to the late 90's and created plots of growth over time, providing valuable context for more detailed studies of air quality, climate changes, and urban planning. (G00-015)
Courtesy: NASA
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| ITEM (9): TRMM - Researchers used the world's first space-based rain radar aboard NASA's Tropical Rainfall Measuring Mission (TRMM) satellite for these studies. Earlier research used ground-based instruments, including rain gauge networks, ground-based radar, or model simulations, to show that urban heat islands can impact local rainfall around cities like St. Louis, Chicago, Mexico City, and Atlanta. Many of these studies were limited to specific cities that had access to relevant data from special observation networks or computer simulations. Satellites broaden the scope of such research by monitoring changes in rainfall patterns over urban areas on global scales over long periods of time.
Courtesy: NASA
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| ITEM (10): Terra - The five sensors aboard Terra are comprehensively measuring our world's climate system--to observe and measure how Earth's atmosphere, cryosphere, lands, oceans, and life all interact. Data from this mission are used in many research and commercial applications. Terra is a vital part of NASA's Earth Science Enterprise, helping us understand and protect our home planet.
Courtesy: NASA
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| ITEM (11): Aqua - Aqua launched May 4, 2002, a powerful Earth observing platform. Aqua's six advanced instruments will look at interrelated geophysical properties of our home planet, with a particular emphasis on water. Comprehensive measurements taken by Aqua's onboard instruments will enable scientists to assess long-term climate change, identify its human and natural causes and advance the development of models for long-term forecasting.
Courtesy: NASA
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| ITEM (12): Aura - Aura will supply the most complete information yet on the health of Earth's atmosphere, once it is launched in spring 2004. This satellite will help scientists understand the causes behind worsening global air quality, our rapidly changing climate, and track the predicted recovery of the ozone layer. Aura will collect data on the composition, chemistry and dynamics of the Earth's upper and lower atmosphere employing multiple instruments on a single satellite. Aura's measurements will follow up on records that began with NASA'S Upper Atmospheric Research Satellite (UARS) and the Total Ozone Mapping Spectrometer (TOMS).
Courtesy: NASA
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