Caption for 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. Credit: NASA
High resolution of normal summer
High resolution of polluted summer
Caption for 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. Credit: NASA
High resolution of coastal city
Caption for 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. Credit: NASA
High resolution of normal winter
High resolution of polluted winter
Caption for 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. Credit: NASA
Caption for Image 5: Satellite Images of Houston Metro Area
These images show the Houston metropolitan area, where buildings, roads and other built surfaces create urban heat islands that can affect local rain patterns. The images were taken by ASTER (Advanced Spaceborne Thermal Emission and Reflection Radiometer), an imaging instrument that is flying on Terra, a satellite launched in December 1999 as part of NASA's Earth Observing System (EOS). Credit: NASA/JPL
Caption for Image 6: Higher Rainfall Rates Downwind of Texas Cities
This image shows areas where urban heat islands influenced higher rainfall rates (in blue) downwind of major cities connected by Interstate 35, known as the I-35 corridor in Texas. The winds that carried clouds and rainfall downwind (in this case, south and east of urban areas) occurred roughly 3.0 kilometers (1.9 miles) above the surface. Rainfall was measured by the precipitation radar instrument on NASA's Tropical Rainfall Measuring Mission (TRMM) satellite. The higher rainfall rates depicted here were derived from measurements of mean monthly rainfall during the warm seasons (May through September) from 1998 through 2000. Credit: Jim Williams, Scientific Visualization Studio, NASA/Goddard Space Flight Center
Caption for Image 7: Higher Rainfall Rates Downwind of Atlanta, Georgia
This image shows areas where urban heat islands influenced higher rainfall rates (in blue) downwind of Atlanta, Georgia. Rainfall was measured by the precipitation radar instrument on NASA's Tropical Rainfall Measuring Mission (TRMM) satellite. The higher rainfall rates depicted here were derived from satellite measurements of mean monthly rainfall during the warm seasons (May through September) from 1998 through 2000. Credit: Jim Williams, Scientific Visualization Studio, NASA/Goddard Space Flight Center
Caption for Item 8: TRMM: Watching Rain to Help Explain
The Tropical Rainfall Measuring Mission (TRMM) is the first Earth Science mission dedicated to studying tropical and subtropical rainfall, precipitation that falls within 35 degrees north and 35 degrees south of the equator. Tropical rainfall comprises more than two-thirds of the world's total. The satellite uses several instruments to detect rainfall including radar, microwave imaging, and lightning sensors. Flying at a low orbital altitude of 217 miles (350 kilometers), TRMM's study of tropical rainfall and attendant processes will help improve our understanding and predictions of global climate change. The Japanese space agency (NASDA) launched the satellite on an H-II rocket from Tanegashima Space Center on November 27, 1997. TRMM data is available to researchers around the world; it is managed by a team at NASA's Goddard Space Flight Center in Greenbelt, Maryland. Credit: NASA
Caption for Item 9: Terra Satellite
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. Credit: NASA
Caption for Item 10: Aqua Satellite
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. Credit: NASA
Caption for Item 11: Aura Satellite
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). Credit: NASA
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