The James Webb Space Telescope Mission

Twenty-six years ago a small committee report, building on earlier studies, expounded a compelling and poetic vision for the future of astronomy, calling for an infrared-optimized space telescope with an aperture of at least $4m$. With the support of their governments in the US, Europe, and Canada, 20,000 people realized that vision as the $6.5m$ James Webb Space Telescope. A generation of astronomers will celebrate their accomplishments for the life of the mission, potentially as long as 20 years, and beyond. This report and the scientific discoveries that follow are extended thank-you notes to the 20,000 team members. The telescope is working perfectly, with much better image quality than expected. In this and accompanying papers, we give a brief history, describe the observatory, outline its objectives and current observing program, and discuss the inventions and people who made it possible. We cite detailed reports on the design and the measured performance on orbit.Comment: Accepted by PASP for the special issue on The James Webb Space Telescope Overview, 29 pages, 4 figure

Climate control of terrestrial carbon exchange across biomes and continents

Peer reviewe

Evaluation of remote sensing based terrestrial productivity from MODIS using regional tower eddy flux network observations

The Moderate Resolution Spectroradiometer (MODIS) sensor has provided near real-time estimates of gross primary production (GPP) since March 2000. We compare four years (2000 to 2003) of satellite-based calculations of GPP with tower eddy CO2 flux-based estimates across diverse land cover types and climate regimes. We examine the potential error contributions from meteorology, leaf area index (LAI)/fPAR, and land cover. The error between annual GPP computed from NASA\u27s Data Assimilation Office\u27s (DAO) and tower-based meteorology is 28%, indicating that NASA\u27s DAO global meteorology plays an important role in the accuracy of the GPP algorithm. Approximately 62% of MOD15-based estimates of LAI were within the estimates based on field optical measurements, although remaining values overestimated site values. Land cover presented the fewest errors, with most errors within the forest classes, reducing potential error. Tower-based and MODIS estimates of annual GPP compare favorably for most biomes, although MODIS GPP overestimates tower-based calculations by 20%-30%. Seasonally, summer estimates of MODIS GPP are closest to tower data, and spring estimates are the worst, most likely the result of the relatively rapid onset of leaf-out. The results of this study indicate, however, that the current MODIS GPP algorithm shows reasonable spatial patterns and temporal variability across a diverse range of biomes and climate regimes. So, while continued efforts are needed to isolate particular problems in specific biomes, we are optimistic about the general quality of these data, and continuation of the MOD17 GPP product will likely provide a key component of global terrestrial ecosystem analysis, providing continuous weekly measurements of global vegetation production

Climate Control of Terrestrial Carbon Exchange across Biomes and Continents

Understanding the relationships between climate and carbon exchange by terrestrial ecosystems is critical to predicate future levels of atmospheric carbon dioxide because of the potential accelerating effects of positive climate-carbon cycle feedbacks1, 2. However, knowledge of even the broad relationships between climate and terrestrial CO2 exchange with the atmosphere on yearly to decadal scales remains highly uncertain. Here we present data describing net ecosystem exchange of carbon (NEE) and climate factors as measured using the eddy covariance method at 132 unique sites including various ecosystems over 6 continents with a total of 583 site-years. With respect to controlling factors we find two distinct groupings of sites: (1) a temperature-limited group where NEE has an exponential relationship with mean annual temperature; and (2) a dryness-limited group where NEE has an inverse exponential relationship with the dryness index7. A strong latitudinal dependence emerges, with 92% of the temperature-limited sites located above 42oN, and 77% of the dryness-limited sites located below 42oN. The sensitivity of NEE to mean annual temperature breaks down at a threshold value of ~16oC, above which no further increase of CO2 uptake with temperature was observed and dryness influence overrules temperature influence. Our findings suggest that (1) net ecosystem carbon exchange is highly limited by mean annual temperature at mid- and high-latitudes, and (2) net ecosystem carbon exchange is highly limited by dryness at low latitudes.JRC.H.2-Air and Climat

The James Webb Space Telescope Mission

Twenty-six years ago a small committee report, building on earlier studies, expounded a compelling and poetic vision for the future of astronomy, calling for an infrared-optimized space telescope with an aperture of at least 4 m. With the support of their governments in the US, Europe, and Canada, 20,000 people realized that vision as the 6.5 m James Webb Space Telescope. A generation of astronomers will celebrate their accomplishments for the life of the mission, potentially as long as 20 yr, and beyond. This report and the scientific discoveries that follow are extended thank-you notes to the 20,000 team members. The telescope is working perfectly, with much better image quality than expected. In this and accompanying papers, we give a brief history, describe the observatory, outline its objectives and current observing program, and discuss the inventions and people who made it possible. We cite detailed reports on the design and the measured performance on orbit