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1. Introduction It is well known that the radiative forcing from carbon dioxide is approximately logarithmic in its concentration, producing about 4 W m −2 of additional global-mean forcing for every doubling. There are, however, two different explanations in the literature for this logarithmic dependence. Given the dominant role that CO 2 plays in global warming, this mechanistic uncertainty merits resolution. Perhaps the most widely accepted explanation is that the logarithmic
1. Introduction It is well known that the radiative forcing from carbon dioxide is approximately logarithmic in its concentration, producing about 4 W m −2 of additional global-mean forcing for every doubling. There are, however, two different explanations in the literature for this logarithmic dependence. Given the dominant role that CO 2 plays in global warming, this mechanistic uncertainty merits resolution. Perhaps the most widely accepted explanation is that the logarithmic
1. Introduction Each year, atmospheric concentrations of carbon dioxide rise and fall through an intra-annual cycle that is associated with the balance between photosynthesis and respiration in the terrestrial biota ( Francey et al. 1995 ; Keeling et al. 1996 ; Morimoto et al. 2000 ). The terrestrial biota can change the amplitude and timing of the intra-annual cycle via several mechanisms including 1) a fertilization effect due to the increased concentration of atmospheric carbon dioxide
1. Introduction Each year, atmospheric concentrations of carbon dioxide rise and fall through an intra-annual cycle that is associated with the balance between photosynthesis and respiration in the terrestrial biota ( Francey et al. 1995 ; Keeling et al. 1996 ; Morimoto et al. 2000 ). The terrestrial biota can change the amplitude and timing of the intra-annual cycle via several mechanisms including 1) a fertilization effect due to the increased concentration of atmospheric carbon dioxide
1. Introduction An increasing part of the world’s population is living in urban areas, where a disproportionate share of natural resources, including fossil fuels, is used. Carbon dioxide (CO 2 ) emissions of cities are an important term of the global carbon budget, but its estimation is mainly based on inventories of fossil fuel consumption and road traffic ( Mensink et al. 2000 ). The amount of carbon sequestered in urban vegetation is, with a few exceptions ( Nowak and Crane 2002 ), largely
1. Introduction An increasing part of the world’s population is living in urban areas, where a disproportionate share of natural resources, including fossil fuels, is used. Carbon dioxide (CO 2 ) emissions of cities are an important term of the global carbon budget, but its estimation is mainly based on inventories of fossil fuel consumption and road traffic ( Mensink et al. 2000 ). The amount of carbon sequestered in urban vegetation is, with a few exceptions ( Nowak and Crane 2002 ), largely
network AgriFlux. The BREB method uses measures of the vertical gradients of air temperature ( T ) and vapor pressure ( e ), along with direct measures of net radiation ( R n ) and the soil heat flux ( G ), to estimate the turbulent fluxes of sensible ( H ) and latent ( λE ) heat. Fluxes of other scalars, such as carbon dioxide ( F c ), can also be measured if their vertical gradients are accurately measured. The BREB method requires that all terms in the energy balance are measured and accounted for
network AgriFlux. The BREB method uses measures of the vertical gradients of air temperature ( T ) and vapor pressure ( e ), along with direct measures of net radiation ( R n ) and the soil heat flux ( G ), to estimate the turbulent fluxes of sensible ( H ) and latent ( λE ) heat. Fluxes of other scalars, such as carbon dioxide ( F c ), can also be measured if their vertical gradients are accurately measured. The BREB method requires that all terms in the energy balance are measured and accounted for
1. Introduction Carbon dioxide (CO 2 ) directly affects the physiology of plants ( Field et al. 1995 ; Ainsworth and Long 2005 ). Stomates, which regulate the fluxes of water vapor and CO 2 at the leaf surface, reduce their opening under an enriched CO 2 environment because they are able to take up CO 2 more efficiently. As a consequence of the reduced stomatal conductance, plants become more water use efficient by transpiring less, which in turn affects the surface energy and water balance
1. Introduction Carbon dioxide (CO 2 ) directly affects the physiology of plants ( Field et al. 1995 ; Ainsworth and Long 2005 ). Stomates, which regulate the fluxes of water vapor and CO 2 at the leaf surface, reduce their opening under an enriched CO 2 environment because they are able to take up CO 2 more efficiently. As a consequence of the reduced stomatal conductance, plants become more water use efficient by transpiring less, which in turn affects the surface energy and water balance
1. Introduction With the increasing concentration of carbon dioxide (CO 2 ) in the atmosphere and its implications for global climate ( Solomon et al. 2007 ), there is a growing need for developing a more detailed description of the various components within the global carbon cycle. Scientific inquiries and analyses now call for data on anthropogenic CO 2 emissions at spatial and temporal scales finer than the countries and years at which emissions inventories have traditionally been conducted
1. Introduction With the increasing concentration of carbon dioxide (CO 2 ) in the atmosphere and its implications for global climate ( Solomon et al. 2007 ), there is a growing need for developing a more detailed description of the various components within the global carbon cycle. Scientific inquiries and analyses now call for data on anthropogenic CO 2 emissions at spatial and temporal scales finer than the countries and years at which emissions inventories have traditionally been conducted
1. Introduction Previous studies of the diurnal variability of carbon dioxide (CO 2 ) focus mainly on surface processes such as photosynthesis and respiration ( Verma et al. 1989 ; Kim and Verma 1990 ; Lloyd and Taylor 1994 ), rather than on the CO 2 exchange between the atmospheric boundary layer (ABL) and the free atmosphere during daytime. This last process is driven by energy generated within the boundary layer, primarily by buoyancy, and shear at the ABL top. Vilà -Guerau de Arellano et
1. Introduction Previous studies of the diurnal variability of carbon dioxide (CO 2 ) focus mainly on surface processes such as photosynthesis and respiration ( Verma et al. 1989 ; Kim and Verma 1990 ; Lloyd and Taylor 1994 ), rather than on the CO 2 exchange between the atmospheric boundary layer (ABL) and the free atmosphere during daytime. This last process is driven by energy generated within the boundary layer, primarily by buoyancy, and shear at the ABL top. Vilà -Guerau de Arellano et
coverage, and thereby can enable a more reliable analysis of long-term atmospheric temperature trends. In particular, since the end of 1970s, atmospheric temperatures for the lower troposphere to the stratosphere have been retrieved through the measurements of the High-Resolution Infrared Radiation Sounder (HIRS) and Microwave Sounding Unit (MSU) on board National Oceanic and Atmospheric Administration (NOAA) operational polar-orbiting satellites. The HIRS and MSU utilize 15- μ m carbon dioxide (CO 2
coverage, and thereby can enable a more reliable analysis of long-term atmospheric temperature trends. In particular, since the end of 1970s, atmospheric temperatures for the lower troposphere to the stratosphere have been retrieved through the measurements of the High-Resolution Infrared Radiation Sounder (HIRS) and Microwave Sounding Unit (MSU) on board National Oceanic and Atmospheric Administration (NOAA) operational polar-orbiting satellites. The HIRS and MSU utilize 15- μ m carbon dioxide (CO 2
1. Introduction Micrometeorological measurements of the net exchange of carbon dioxide (CO 2 ), water vapor, and energy between terrestrial ecosystems and the atmosphere are now being made routinely at sites worldwide (e.g., the AmeriFlux, EuroFlux, and AsiaFlux networks) to determine the role of terrestrial ecosystems in the global carbon cycle ( Baldocchi et al. 2001 ; Anthoni et al. 2004 ). Cropland represents about 12% of the earth’s surface ( Wood et al. 2000 ; Verma et al. 2005 ) and
1. Introduction Micrometeorological measurements of the net exchange of carbon dioxide (CO 2 ), water vapor, and energy between terrestrial ecosystems and the atmosphere are now being made routinely at sites worldwide (e.g., the AmeriFlux, EuroFlux, and AsiaFlux networks) to determine the role of terrestrial ecosystems in the global carbon cycle ( Baldocchi et al. 2001 ; Anthoni et al. 2004 ). Cropland represents about 12% of the earth’s surface ( Wood et al. 2000 ; Verma et al. 2005 ) and
1. Introduction Although a majority of global anthropogenic carbon dioxide (CO 2 ) emissions originate from urban areas (e.g., Satterthwaite 2008 ), few studies have investigated CO 2 mixing ratios in the urban boundary layer (UBL). Observations are challenging because heights of tower platforms that could support in situ CO 2 mixing ratio measurements in urban areas are often too low (located in the surface layer) and airborne measurements tend to be labor intensive and expensive. Satellite
1. Introduction Although a majority of global anthropogenic carbon dioxide (CO 2 ) emissions originate from urban areas (e.g., Satterthwaite 2008 ), few studies have investigated CO 2 mixing ratios in the urban boundary layer (UBL). Observations are challenging because heights of tower platforms that could support in situ CO 2 mixing ratio measurements in urban areas are often too low (located in the surface layer) and airborne measurements tend to be labor intensive and expensive. Satellite
