Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “BC”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 163 records · Page 9
All sourcesNASA NTRSDOE OSTI
NASA NTRS1999

Multi-Wavelength Superoutburst Observations of T Leonis

We present results of simultaneous superoutburst observations in the X-ray, Extreme Ultraviolet (EUV), optical, and IR bands of the tremendous outburst amplitude dwarf novae T Leonis. Near peak luminosity, a single blackbody represents a good fit to T Leo's observed continuum in the EUV spectral region, yielding a boundary layer temperature of 71,000 to 97,000K. Inclusion of the longer wavelength observations, UV to the IR, indicates that a blackbody fit is inappropriate. A single temperature fit to only the UV and red-ward data for T Leo works well, but yields a much lower temperature, near 28,000K. Using our own observations and previously obtained EUV, UV and optical (super)outburst observations for the dwarf novae U Gem and SS Cyg, the SU UMa star VW Hyi, and the TOADS, TV Crv, BC UMa, and SW UMa, we find that in all cases, high energy observations yield high temperature, small emitting regions, while fits to UV and red-ward data produce cooler temperatures from much larger emitting regions. These results are consistent with the idea that high energy data provide a direct measurement of the boundary layer while the lower energy data measure a much larger, multi-temperature region, likely to be dominated by the outburst heated inner accretion disk. High energy outburst observations show that the boundary layer temperature decreases with decreasing orbital period and UV outburst observations provide evidence for a missing or weak inner disk in the TOADs. We present a simple model of mass accretion onto the white dwarf during (super)outburst which can account for the observed correlation between temperature.

Howell, Steve B.↗
NASA NTRS1999

Interrelationships Between Aerosol Characteristics and Light Scattering During Late-winter in a Eastern Mediterranean Arid Environment

An intensive field campaign involving measurement of various aerosol physical, chemical, and radiative properties was conducted at Sde Boker in the Negev Desert of Israel, from 18 February to 15 March 1997. Nephelometer measurements gave average background scattering coefficient values of about 25 M/m at 550 nm wavelength, but strong dust events caused the value of this parameter to rise up to about 800 M/m Backscattering fractions did not depend on aerosol loading, and generally fell in the range of 0.1 to 0.25, comparable to values reported for marine and Arctic environments. Chemical analysis of the aerosol revealed that, in the coarse size range (2 - 10 micrometer equivalent aerodynamic diameter (EAD)), calcium (Ca) was by far the most abundant element followed by silicon (Si), both of which are indicators for mineral dust. In the fine size fraction (< 2 micrometers EAD), sulfur (S) generally was the dominant element, except during high dust episodes when Ca and Si were again the most abundant. Furthermore, fine black carbon (BC) correlates with S, suggesting that they may have originated from the same sources or source regions. An indication of the short-term effect of aerosol loading on radiative forcing was provided by measurements of global and diffuse solar radiation, which showed that during high turbidity periods (strong dust events) almost all of the solar radiation reaching the area is scattered or absorbed.

Ichoku, C.↗
NASA NTRS1999

Two 1999 Dates Worth Noting

Two dates in 1999 can serve as pivots for space-related educational outreach. On August 11 a total solar eclipse will sweep across Europe and also across the Near East, where it will come remarkably close to matching the ancient eclipse (probably in 129 BC) used by Hipparchus to estimate the distance of the Moon. Using published eclipse data, students may conduct a similar calculation for 1999 and in the process obtain insights about astronomy, history and the way scientists work. October 19, 1999 will be the 100th anniversary of the day when a teen-age Robert Goddard climbed a cherry tree near the Worcester home where his family was staying, intending to prune it. Sitting in that tree, Goddard began daydreaming about space flight, and by the time he came down he had resolved to dedicate his life to implementing that dream. He later marked that day as "Anniversary day," a personal holiday. Material on both subjects can be reached from http://www-spof.gsfc.nasa.gov/stargaze/Sintro.htm, sections 8a and 26. The section on Goddard includes his experiments with a ballistic pendulum and the DeLaval nozzle, which laid the essential scientific foundation of spaceflight and which is also suitable for classroom presentation.

Stern, David P.↗
NASA NTRS1998

Formal Modeling of Multi-Agent Systems using the Pi-Calculus and Epistemic Logic

Multi-agent systems have become important recently in computer science, especially in artificial intelligence (AI). We allow a broad sense of agent, but require at least that an agent has some measure of autonomy and interacts with other agents via some kind of agent communication language. We are concerned in this paper with formal modeling of multi-agent systems, with emphasis on communication. We propose for this purpose to use the pi-calculus, an extension of the process algebra CCS. Although the literature on the pi-calculus refers to agents, the term is used there in the sense of a process in general. It is our contention, however, that viewing agents in the AI sense as agents in the pi-calculus sense affords significant formal insight. One formalism that has been applied to agents in the AI sense is epistemic logic, the logic of knowledge. The success of epistemic logic in computer science in general has come in large part from its ability to handle concepts of knowledge that apply to groups. We maintain that the pi-calculus affords a natural yet rigorous means by which groups that are significant to epistemic logic may be identified, encapsulated, structured into hierarchies, and restructured in a principled way. This paper is organized as follows: Section 2 introduces the pi-calculus; Section 3 takes a scenario from the classical paper on agent-oriented programming [Sh93] and translates it into a very simple subset of the n-calculus; Section 4 then shows how more sophisticated features of the pi-calculus may bc brought into play; Section 5 discusses how the pi-calculus may be used to define groups for epistemic logic; and Section 6 is the conclusion.

Rorie, Toinette↗
NASA NTRS2001

Recent Advances in Maya Studies Using Remotely Sensed Data

The Peten region of northern Guatemala is one of the last places on earth where major archeological sites remain to be discovered. It was in this region that the Maya civilization began, flourished, and abruptly disappeared. Remote sensing technology is helping to locate and map ancient Maya sites that are threatened today by accelerating deforestation and looting. Thematic Mapper and IKONOS satellite and airborne Star3i radar data, combined with Global Positioning System (GPS) technology, are successfully detecting ancient Maya features such as cities, roadways, canals, and water reservoirs. Satellite imagery is also being used to map the bajos, which are seasonally flooded swamps that cover over 40% of the land surface. The use of baJos for farming has been a source of debate within the professional community for many years. But the recent detection and verification of cultural features within the baJo system by our research team are providing conclusive evidence that the ancient Maya had adapted well to wetland environments from the earliest times and utilized them until the time of the Maya collapse. The combination of water management and baJo farming is an important resource for the future of the current inhabitants who are experiencing rapid population growth. Remote sensing imagery is also demonstrating that in the Preclassic period (600 BC- AD 250), the Maya had already achieved a high organizational level as evidenced by the construction of massive temples and an elaborate inter-connecting roadway system. Although they experienced several setbacks such as droughts and hurricanes, the Maya nevertheless managed the delicate forest ecosystem successfully for several centuries. However, around AD 800, something happened to the Maya to cause their rapid decline and eventual disappearance from the region. The evidence indicates that at this time there was increased climatic dryness, extensive deforestation, overpopulation, and widespread warfare. This raises a relevant question today-namely, how severe do internal stresses in a civilization have to become before relatively minor climate shifts can cause a widespread cultural collapse?

Sever, Tom↗
NASA NTRS2001

Recent Advances in Maya Studies Using Remotely Sensed Data

The Peten region of northern Guatemala is one of the last places on earth where major archeological sites remain to be discovered. It was in this region that the Maya civilization began, flourished, and abruptly disappeared. Remote sensing technology is helping to locate and map ancient Maya sites that are threatened today by accelerating deforestation and looting. Thematic Mapper and IKONOS satellite and airborne Star3i radar data, combined with Global Positioning System (GPS) technology, are successfully detecting ancient Maya features such as cities, roadways, canals, and water reservoirs. Satellite imagery is also being used to map the baJos, which are seasonally flooded swamps that cover over 40% of the land surface. The use of bajos for farming has been a source of debate within the professional community for many years. But the recent detection and verification of cultural features within the bajo system by our research team are providing conclusive evidence that the ancient Maya had adapted well to wetland environments from the earliest times and utilized them until the time of the Maya collapse. The combination of water management and bajo farming is an important resource for the future of the current inhabitants who are experiencing rapid population growth. Remote sensing imagery is also demonstrating that in the Preclassic period (600 BC- AD 250), the Maya had already achieved a high organizational level as evidenced by the construction of massive temples and an elaborate inter-connecting roadway system. Although they experienced several setbacks such as droughts and hurricanes, the Maya nevertheless managed the delicate forest ecosystem successfully for several centuries. However, around AD 800, something happened to the Maya to cause their rapid decline and eventual disappearance from the region. The evidence indicates that at this time there was increased climatic dryness, extensive deforestation, overpopulation, and widespread warfare. This raises a relevant question today-namely, how severe do internal stresses in a civilization have to become before relatively minor climate shifts can cause a widespread cultural collapse?

Sever, Tom↗
NASA NTRS2002

Mapping The Ancient Maya Landscape From Space

The Peten region of northern Guatemala is one of the last places on earth where major archeological sites remain to be discovered. It was in this region that the Maya civilization began, flourished, and abruptly disappeared. Remote sensing technology is helping to locate and map ancient Maya sites that are threatened today by accelerating deforestation and looting. Thematic Mapper and IKONOS satellite and airborne Star3-I radar data, combined with Global Positioning System (GPS) technology, are successfully detecting ancient Maya features such as cities, roadways, canals, and water reservoirs. Satellite imagery is also being used to map the bajos, which are seasonally flooded swamps that cover over 40% of the land surface. The use of bajos for farming has been a source of debate within the professional community for many years. But the recent detection and verification of cultural features within the bajo system by our research team are providing conclusive evidence that the ancient Maya had adapted well to wetland environments from the earliest times and utilized them until the time of the Maya collapse. The use of the bajos for farming is also an important resource for the future of the current inhabitants who are experiencing rapid population growth. Remote sensing imagery is also demonstrating that in the Preclassic period (600 BC- AD 250), the Maya had already achieved a high organizational level as evidenced by the construction of massive temples and an elaborate inter-connecting roadway system. Although they experienced several setbacks such as droughts and hurricanes, the Maya nevertheless managed the delicate forest ecosystem successfully for several centuries. However, around AD 800, something happened to the Maya to cause their rapid decline and eventual disappearance from the region. The evidence indicates that at this time there was increased climatic dryness, extensive deforestation, overpopulation, and widespread warfare. This raises a question that is relevant to the contemporary world-namely, how severe do internal stresses in a civilization have to become before relatively minor climate shifts can trigger a widespread cultural collapse?

Sever, Tom↗
NASA NTRS2003

Radiative Forcing of the Lower Stratosphere over the Arctic by Light Absorbing Particles

Light absorbing particles (LAP), such as soot and dust, change the thermodynamic structure of the atmosphere and contribute to regional and global climate change. The lower stratosphere (LS) is particularly sensitive to the presence of LAP since the lifetime of particles in the LS may extend from months to years, in contrast to tropospheric lifetimes of at most a few days. The source of particles in the LS may be aircraft, meteorites or emissions from tropospheric sources. There has been a lack, however, of accurate, quantitative measurements made with sufficiently sensitive instruments. This limits our understanding of the origin and lifetime of aerosols in this region of the atmosphere. Here we present recent measurements in the Arctic UT/LS with a new, highly sensitive instrument that has detected black carbon (BC) mass concentrations of 20-1000 ng m(exp -3) that are 10-1000 times larger than those reported in previous studies and are at least 30 times larger than predicted masses based on fuel consumption by commercial aircraft that fly in these regions. Scattering and absorption of solar and terrestrial radiation by the particles in a layer from 8- 12 Km leads to a negative net forcing of -0.5 W sq m at the top of the atmosphere and 9C of heating in this layer during the average aerosol lifetime at these altitudes. The new measurements suggest that the influence of aircraft emissions have been underestimated or that aircraft may not be the only significant source of light absorbing particles in the UT/LS. The presence of these aerosols can cause local changes in the thermal structure of the lower stratosphere and a subsequent modification of stratosphere/tropopause exchange of gases and particles.

Baumgardner, D.↗
NASA NTRS2003

Boundary Conditions of the Heliosphere

As described in the Revised Task Statement for this grant (submitted following the award at a reduced budget), my role in these investigations is to focus on the theoretical calculations relevant to the ionization state and dust content of the Local Cloud that surrounds the Solar System. An important motivation for our investigations is to aid in the interpretation of pick-up ion (PUI) and anomalous cosmic ray (ACR) observations which depends on knowledge of the flux of neutral atoms of various elements into the heliosphere. This flux depends on the ionization and elemental abundances of the gas of the Local Cloud. We have made substantial progress in our program to understand the ionization of the Local Cloud. Our steady state photoionization models are remarkably successful in accounting for the ionization observed both by line of sight (column density) observations towards nearby stars and in situ measurements. By lifting some of the simplifying assumptions in our earlier modeling we hope to make further progress in this understanding. In future work on this project we will continue our exploration of photoionization models, focusing on making sense of the differences between the LIC and the BC. In addition we will explore the effects of altered abundances in the hot gas on the ionization and thermal balance in the LIC.

Frisch, Priscilla C.↗
NASA NTRS2003

Black Carbon in Estuarine and Coastal Ocean Dissolved Organic Matter

Analysis of high-molecular-weight dissolved organic matter (DOM) from two estuaries in the northwest Atlantic Ocean reveals that black carbon (BC) is a significant component of previously uncharacterized DOM, suggesting that river-estuary systems are important exporters of recalcitrant dissolved organic carbon to the ocean.

Mannino, Antonio↗
NASA NTRS2004

Boundary Conditions of the Heliosphere: Fluctuations in Nearby Interstellar Gas

We have made substantial progress in our program to understand the ionization of the Local Cloud. Our steady state photoionization models are remarkably successful in accounting for the ionization observed both by line of sight (column density) observations towards nearby stars and in situ measurements. By lifting some of the simplifying assumptions in our earlier modeling we are making further progress in this understanding. In future work on this project we will continue our exploration of photoionization models, focusing on making sense of the differences between the LIC and the BC.

Slavin, Jonathan↗
NASA NTRS2004

Creating and Perpetuating Social Memory across the Ancient Cost Rican Landscape

For most of the time that Native Americans lived in ancient Costa Rica, their travel across the landscape was task-oriented and thus sufficiently randomized to leave no detectable trace. That changed about 500 BC in the Arenal area when people separated their cemeteries from their villages, and travel between them was ritually mediated by travel along the same path, in single file, in as straight a line as possible. The inadvertent erosion over centuries of use entrenched paths 2 or more meters deep, and we believe the cultural standard developed that the preferred way of entering a special place was by an entrenched path. People created and perpetuated social memory across their landscapes with generation after generation of use. The construction of meaning developed as the paths entrenched, ultimately embedding that meaning deep in people s belief systems as well as literally embedding it in the landscape. the Arenal area, a series of chiefdoms did develop east of the area at about AD 1000. To satisfy their need for monumentality, we suggest here that chiefs chose the proper entrenched entryway as exemplified in the Arenal area, for elaboration. On the rocky slopes of the volcanoes monumental entryways were built of stone, and on the fine alluvial plains they were of earthen construction. For instance, the radiating entrenched roads entering Cutris are about 4 km long and as wide as 50 meters, and many meters deep.

Sheets, Payson↗
NASA NTRS2005

X-Ray Spectroscopy of Optically Bright Planets using the Chandra Observatory

Since its launch in July 1999, Chandra's Advanced CCD Imaging Spectrometer (ACIS) has observed several planets (Venus, Mars, Jupiter and Saturn) and 6 comets. At 0.5 arc-second spatial resolution, ACIS detects individual x-ray photons with good quantum efficiency (25% at 0.6 KeV) and energy resolution (20% FWHM at 0.6 KeV). However, the ACIS CCDs are also sensitive to optical and near-infrared light, which is absorbed by optical blocking filters (OBFs) that eliminate optical contamination from all but the brightest extended sources, e.g., planets. .Jupiter at opposition subseconds approx.45 arc-seconds (90 CCD pixels.) Since Chandra is incapable of tracking a moving target, the planet takes 10 - 20 kiloseconds to move across the most sensitive ACIS CCD, after which the observatory must be re-pointed. Meanwhile, the OBF covering that CCD adds an opt,ical signal equivalent to approx.110 eV to each pixel that lies within thc outline of the Jovian disk. This has three consequences: (1) the observatory must be pointed away from Jupiter while CCD bias maps are constructed; (2) most x-rays from within the optical image will be misidentified as charged-particle background and ignored; and (3) those x-rays that are reported will bc assigned anomalously high energies. The same also applies to thc other planets, but is less serious since they are either dimmer at optical wavelengths, or they show less apparent motion across the sky, permitting reduced CCD exposure times: the optical contamination from Saturn acids approx.15 eV per pixel, and from Mars and Venus approx.31 eV. After analyzing a series of short .Jupiter observations in December 2000, ACIS parameters were optimized for the February 2003 opposition. CCD bias maps were constructed while Chandra pointed away from Jupiter, and the subsequent observations employed on-board software to ignore any pixel that contained less charge than that expected from optical leakage. In addition, ACIS was commanded to report 5 x 5 arrays of pixel values surrounding each x-ray event, and the outlying values were employed during ground processing to correct for the optical contamination.

Ford, P. G.↗
NASA NTRS2004

Statistical and Prediction modeling of the Ka Band Using Experimental Results from ACTS Propagation Terminals at 20.185 and 27.505 GHZ

With the increase in demand for wireless communication services, most of the operating frequency bands have become very congested. The increase of wireless costumers is only fractional contribution to this phenomenon. The demand for more services such as video streams and internet explorer which require a lot of band width has been a more significant contributor to the congestion in a communication system. One way to increase the amount of information or data per unit of time transmitted with in a wireless communication system is to use a higher radio frequency. However in spite the advantage available in the using higher frequency bands such as, the Ka-band, higher frequencies also implies short wavelengths. And shorter wavelengths are more susceptible to rain attenuation. Until the Advanced Communication Technology Satellite (ACTS) was launched, the Ka- band frequency was virtually unused - the majority of communication satellites operated in lower frequency bands called the C- and Ku- bands. Ka-band is desirable because its higher frequency allows wide bandwidth applications, smaller spacecraft and ground terminal components, and stronger signal strength. Since the Ka-band is a high frequency band, the millimeter wavelengths of the signals are easily degraded by rain. This problem known as rain fade or rain attenuation The Advanced Communication Technology Satellite (ACTS) propagation experiment has collected 5 years of Radio Frequency (RF) attenuation data from December 1993 to November 1997. The objective of my summer work is to help develop the statistics and prediction techniques that will help to better characterize the Ka Frequency band. The statistical analysis consists of seasonal and cumulative five-year attenuation statistics for the 20.2 and 27.5 GHz. The cumulative five-year results give the link outage that occurs for a given link margin. The experiment has seven ground station terminals that can be attributed to a unique rain zone climate. The locations are White Sands, NM, Tampa, Fly Clarksburg, MD, Norman, OK, Ft. Collins, COY Vancouver, BC, and Fairbanks, AK. The analysis will help us to develop and define specific parameters that will help system engineers develop the appropriated instrumentation and structure for a Ka-band wireless communication systems and networks.

Ogunwuyi, Oluwatosin O.↗
NASA NTRS2006

Enhancing the ATIC Charge Resolution

The Advanced Thin Ionization Calorimeter (ATIC) experiment measures the energy spectra of elements, from H to Fe, in the energy region from about 100 GeV to tens of TeV. The ATIC instrument was flown twice in long-duration balloon flights around the South Pole; the ATIC-1 test flight during Dec. 2000 - Jan. 2001 and the ATIC-2 science flight during Dec. 2002 - Jan. 2003. Analyses of both datasets have, to date, relied upon the highly segmented Silicon Matrix (SiM) detector to separate the incident cosmic ray from the calorimeter backscatter and to identify the charge. This method has worked well, enabling ATIC to separate protons from helium and to resolve all the major species up through iron. This charge resolution can be significantly improved by restricting the analysis to particle trajectories that pass through two SiM pixels at the cost of using only a fraction of the potential instrument geometry. However, immediately below the SiM is the two layer SI hodoscope (x, y) consisting of Bicron BC-408 plastic scintillator 2 cm wide, 1 cm thick, 88.2 cm long strips viewed by Hamamatsu R5611 photomultiplier tubes on each end of each strip. The primary purpose of the ATIC hodoscopes is to provide a fast trigger, and each hodoscope includes two crossed layers of strips (42 per layer in the case of Sl) providing supplemental particle trajectory information. The hodoscope readout electronics were designed to provide reasonable charge resolution over the dynamic range from protons through iron. This presentation discusses the S 1 hodoscope energy deposit calibrations, examines the charge resolution possible with this detector and investigates combining the S1 and SiM charge measurements to improve the overall ATIC charge resolution while minimizing degradation of the instrument geometry.

Guzik, T. G.↗
NASA NTRS2007

Trans-Pacific Transport of Saharan Dust to Western North America: A Case Study

The first documented case of long range transport of Saharan dust over a pathway spanning Asia and the Pacific to Western North America is described. Crustal material generated by North African dust storms during the period 28 February - 3 March 2005 reached western Canada on 13-14 March 2005 and was observed by lidar and sunphotometer in the Vancouver region and by high altitude aerosol instrumentation at Whistler Peak. Global chemical models (GEOS-CHEM and NRL NAAPS) confirm the transport pathway and suggest source attribution was simplified in this case by the distinct, and somewhat unusual, lack of dust activity over Eurasia (Gobi and Takla Makan deserts) at this time. Over western North America, the dust layer, although subsiding close to the boundary layer, did not appear to contribute to boundary layer particulate matter concentrations. Furthermore, sunphotometer observations (and associated inversion products) suggest that the dust layer had only subtle optical impact (Aerosol Optical Thickness (Tau(sub a500)) and Angstrom exponent (Alpha(sub 440-870) were 0.1 and 1.2 respectively) and was dominated by fine particulate matter (modes in aerodynamic diameter at 0.3 and 2.5microns). High Altitude observations at Whistler BC, confirm the crustal origin of the layer (rich in Ca(++) ions) and the bi-modal size distribution. Although a weak event compared to the Asian Trans-Pacific dust events of 1998 and 2001, this novel case highlights the possibility that Saharan sources may contribute episodically to the aerosol burden in western North America.

Kendry, Ian G. M.↗
NASA NTRS2007

Precipitation Measurements from Space: The Global Precipitation Measurement Mission

Water is fundamental to the life on Earth and its phase transition between the gaseous, liquid, and solid states dominates the behavior of the weather/climate/ecological system. Precipitation, which converts atmospheric water vapor into rain and snow, is central to the global water cycle. It regulates the global energy balance through interactions with clouds and water vapor (the primary greenhouse gas), and also shapes global winds and dynamic transport through latent heat release. Surface precipitation affects soil moisture, ocean salinity, and land hydrology, thus linking fast atmospheric processes to the slower components of the climate system. Precipitation is also the primary source of freshwater in the world, which is facing an emerging freshwater crisis in many regions. Accurate and timely knowledge of global precipitation is essential for understanding the behavior of the global water cycle, improving freshwater management, and advancing predictive capabilities of high-impact weather events such as hurricanes, floods, droughts, and landslides. With limited rainfall networks on land and the impracticality of making extensive rainfall measurements over oceans, a comprehensive description of the space and time variability of global precipitation can only be achieved from the vantage point of space. This presentation will examine current capabilities in space-borne rainfall measurements, highlight scientific and practical benefits derived from these observations to date, and provide an overview of the multi-national Global Precipitation Measurement (GPM) Mission scheduled to bc launched in the early next decade.

Hou, Arthur Y.↗
NASA NTRS2007

Future Climate Impacts of Direct Radiative Forcing Anthropogenic Aerosols, Tropospheric Ozone, and Long-lived Greenhouse Gases

Long-lived greenhouse gases (GHGs) are the most important driver of climate change over the next century. Aerosols and tropospheric ozone (O3) are expected to induce significant perturbations to the GHG-forced climate. To distinguish the equilibrium climate responses to changes in direct radiative forcing of anthropogenic aerosols, tropospheric ozone, and GHG between present day and year 2100, four 80-year equilibrium climates are simulated using a unified tropospheric chemistry-aerosol model within the Goddard Institute for Space Studies (GISS) general circulation model (GCM) 110. Concentrations of sulfate, nitrate, primary organic (POA) carbon, secondary organic (SOA) carbon, black carbon (BC) aerosols, and tropospheric ozone for present day and year 2100 are obtained a priori by coupled chemistry-aerosol GCM simulations, with emissions of aerosols, ozone, and precursors based on the Intergovernmental Panel on Climate Change (IPCC) Special Report on Emissions Scenario (SRES) A2. Changing anthropogenic aerosols, tropospheric ozone, and GHG from present day to year 2100 is predicted to perturb the global annual mean radiative forcing by +0.18 (considering aerosol direct effects only), +0.65, and +6.54 W m(sup -2) at the tropopause, and to induce an equilibrium global annual mean surface temperature change of +0.14, +0.32, and +5.31 K, respectively, with the largest temperature response occurring at northern high latitudes. Anthropogenic aerosols, through their direct effect, are predicted to alter the Hadley circulation owing to an increasing interhemispheric temperature gradient, leading to changes in tropical precipitation. When changes in both aerosols and tropospheric ozone are considered, the predicted patterns of change in global circulation and the hydrological cycle are similar to those induced by aerosols alone. GHG-induced climate changes, such as amplified warming over high latitudes, weakened Hadley circulation, and increasing precipitation over the Tropics and high latitudes, are consistent with predictions of a number of previous GCM studies. Finally, direct radiative forcing of anthropogenic aerosols is predicted to induce strong regional cooling over East and South Asia. Wintertime rainfall over southeastern China and the Indian subcontinent is predicted to decrease because of the increased atmospheric stability and decreased surface evaporation, while the geographic distribution of precipitation is also predicted to be altered as a result of aerosol-induced changes in wind flow.

Chen, Wei-Ting↗