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John H. Seinfeld
,
Ralph A. Kahn
,
Theodore L. Anderson
,
Robert J. Charlson
,
Roger Davies
,
David J. Diner
,
John A. Ogren
,
Stephen E. Schwartz
, and
Bruce A. Wielicki

Aerosols are involved in a complex set of processes that operate across many spatial and temporal scales. Understanding these processes, and ensuring their accurate representation in models of transport, radiation transfer, and climate, requires knowledge of aerosol physical, chemical, and optical properties and the distributions of these properties in space and time. To derive aerosol climate forcing, aerosol optical and microphysical properties and their spatial and temporal distributions, and aerosol interactions with clouds, need to be understood. Such data are also required in conjunction with size-resolved chemical composition in order to evaluate chemical transport models and to distinguish natural and anthropogenic forcing. Other basic parameters needed for modeling the radiative influences of aerosols are surface reflectivity and three-dimensional cloud fields. This large suite of parameters mandates an integrated observing and modeling system of commensurate scope. The Progressive Aerosol Retrieval and Assimilation Global Observing Network (PARAGON) concept, designed to meet this requirement, is motivated by the need to understand climate system sensitivity to changes in atmospheric constituents, to reduce climate model uncertainties, and to analyze diverse collections of data pertaining to aerosols. This paper highlights several challenges resulting from the complexity of the problem. Approaches for dealing with them are offered in the set of companion papers.

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Robert E. Dickinson
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Stephen E. Zebiak
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Jeffrey L. Anderson
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Maurice L. Blackmon
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Cecelia De Luca
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Timothy F. Hogan
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Mark Iredell
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Ming Ji
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Ricky B. Rood
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Max J. Suarez
, and
Karl E. Taylor

A common modeling infrastructure ad hoc working group evolved from an NSF/NCEP workshop in 1998, in recognition of the need for the climate and weather modeling communities to develop a more organized approach to building the software that underlies modeling and data analyses. With its significant investment of pro bono time, the working group made the first steps in this direction. It suggested standards for model data and model physics and explored the concept of a modeling software framework. An overall software infrastructure would facilitate separation of the scientific and computational aspects of comprehensive models. Consequently, it would allow otherwise isolated scientists to effectively contribute to core U.S. modeling activities, and would provide a larger market to computational scientists and computer vendors, hence encouraging their support.

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Randolph H. Ware
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David W. Fulker
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Seth A. Stein
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David N. Anderson
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Susan K. Avery
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Richard D. Clark
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Kelvin K. Droegemeier
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Joachim P. Kuettner
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J. Bernard Minster
, and
Soroosh Sorooshian

“SuomiNet,” a university-based, real-time, national Global Positioning System (GPS) network, is being developed for atmospheric research and education with funding from the National Science Foundation and with cost share from collaborating universities. The network, named to honor meteorological satellite pioneer Verner Suomi, will exploit the recently shown ability of ground-based GPS receivers to make thousands of accurate upper- and lower-atmospheric measurements per day. Phase delays induced in GPS signals by the ionosphere and neutral atmosphere can be measured with high precision simultaneously along a dozen or so GPS ray paths in the field of view. These delays can be converted into integrated water vapor (if surface pressure data or estimates are available) and total electron content (TEC), along each GPS ray path. The resulting continuous, accurate, all-weather, real-time GPS moisture data will help advance university research in mesoscale modeling and data assimilation, severe weather, precipitation, cloud dynamics, regional climate, and hydrology. Similarly, continuous, accurate, all-weather, real-time TEC data have applications in modeling and prediction of severe terrestrial and space weather, detection and forecasting of low-altitude ionospheric scintillation activity and geomagnetic storm effects at ionospheric midlatitudes, and detection of ionospheric effects induced by a variety of geophysical events. SuomiNet data also have potential applications in coastal meteorology, providing ground truth for satellite radiometry, and detection of scintillation associated with atmospheric turbulence in the lower troposphere. The goal of SuomiNet is to make large amounts of spatially and temporally dense GPS-sensed atmospheric data widely available in real time, for academic research and education. Information on participation in SuomiNet is available via www.unidata.ucar.edu/suominet.

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C. L. Reddington
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K. S. Carslaw
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P. Stier
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N. Schutgens
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H. Coe
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D. Liu
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J. Allan
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J. Browse
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K. J. Pringle
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L. A. Lee
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M. Yoshioka
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J. S. Johnson
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L. A. Regayre
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D. V. Spracklen
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G. W. Mann
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A. Clarke
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M. Hermann
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S. Henning
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H. Wex
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T. B. Kristensen
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W. R. Leaitch
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U. Pöschl
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D. Rose
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M. O. Andreae
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J. Schmale
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Y. Kondo
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N. Oshima
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J. P. Schwarz
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A. Nenes
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B. Anderson
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G. C. Roberts
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J. R. Snider
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C. Leck
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P. K. Quinn
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X. Chi
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A. Ding
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J. L. Jimenez
, and
Q. Zhang

Abstract

The largest uncertainty in the historical radiative forcing of climate is caused by changes in aerosol particles due to anthropogenic activity. Sophisticated aerosol microphysics processes have been included in many climate models in an effort to reduce the uncertainty. However, the models are very challenging to evaluate and constrain because they require extensive in situ measurements of the particle size distribution, number concentration, and chemical composition that are not available from global satellite observations. The Global Aerosol Synthesis and Science Project (GASSP) aims to improve the robustness of global aerosol models by combining new methodologies for quantifying model uncertainty, to create an extensive global dataset of aerosol in situ microphysical and chemical measurements, and to develop new ways to assess the uncertainty associated with comparing sparse point measurements with low-resolution models. GASSP has assembled over 45,000 hours of measurements from ships and aircraft as well as data from over 350 ground stations. The measurements have been harmonized into a standardized format that is easily used by modelers and nonspecialist users. Available measurements are extensive, but they are biased to polluted regions of the Northern Hemisphere, leaving large pristine regions and many continental areas poorly sampled. The aerosol radiative forcing uncertainty can be reduced using a rigorous model–data synthesis approach. Nevertheless, our research highlights significant remaining challenges because of the difficulty of constraining many interwoven model uncertainties simultaneously. Although the physical realism of global aerosol models still needs to be improved, the uncertainty in aerosol radiative forcing will be reduced most effectively by systematically and rigorously constraining the models using extensive syntheses of measurements.

Open access
L. L. Pan
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E. L. Atlas
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R. J. Salawitch
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S. B. Honomichl
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J. F. Bresch
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W. J. Randel
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E. C. Apel
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R. S. Hornbrook
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A. J. Weinheimer
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D. C. Anderson
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S. J. Andrews
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S. Baidar
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S. P. Beaton
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T. L. Campos
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L. J. Carpenter
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D. Chen
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B. Dix
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V. Donets
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S. R. Hall
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T. F. Hanisco
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C. R. Homeyer
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L. G. Huey
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J. B. Jensen
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L. Kaser
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D. E. Kinnison
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T. K. Koenig
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J.-F. Lamarque
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C. Liu
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J. Luo
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Z. J. Luo
,
D. D. Montzka
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J. M. Nicely
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R. B. Pierce
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D. D. Riemer
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T. Robinson
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P. Romashkin
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A. Saiz-Lopez
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S. Schauffler
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O. Shieh
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M. H. Stell
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K. Ullmann
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G. Vaughan
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R. Volkamer
, and
G. Wolfe

Abstract

The Convective Transport of Active Species in the Tropics (CONTRAST) experiment was conducted from Guam (13.5°N, 144.8°E) during January–February 2014. Using the NSF/NCAR Gulfstream V research aircraft, the experiment investigated the photochemical environment over the tropical western Pacific (TWP) warm pool, a region of massive deep convection and the major pathway for air to enter the stratosphere during Northern Hemisphere (NH) winter. The new observations provide a wealth of information for quantifying the influence of convection on the vertical distributions of active species. The airborne in situ measurements up to 15-km altitude fill a significant gap by characterizing the abundance and altitude variation of a wide suite of trace gases. These measurements, together with observations of dynamical and microphysical parameters, provide significant new data for constraining and evaluating global chemistry–climate models. Measurements include precursor and product gas species of reactive halogen compounds that impact ozone in the upper troposphere/lower stratosphere. High-accuracy, in situ measurements of ozone obtained during CONTRAST quantify ozone concentration profiles in the upper troposphere, where previous observations from balloonborne ozonesondes were often near or below the limit of detection. CONTRAST was one of the three coordinated experiments to observe the TWP during January–February 2014. Together, CONTRAST, Airborne Tropical Tropopause Experiment (ATTREX), and Coordinated Airborne Studies in the Tropics (CAST), using complementary capabilities of the three aircraft platforms as well as ground-based instrumentation, provide a comprehensive quantification of the regional distribution and vertical structure of natural and pollutant trace gases in the TWP during NH winter, from the oceanic boundary to the lower stratosphere.

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David J. Diner
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Robert T. Menzies
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Ralph A. Kahn
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Theodore L. Anderson
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Jens Bösenberg
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Robert J. Charlson
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Brent N. Holben
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Chris A. Hostetler
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Mark A. Miller
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John A. Ogren
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Graeme L. Stephens
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Omar Torres
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Bruce A. Wielicki
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Philip J. Rasch
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Larry D. Travis
, and
William D. Collins

A comprehensive and cohesive aerosol measurement record with consistent, well-understood uncertainties is a prerequisite to understanding aerosol impacts on long-term climate and environmental variability. Objectives to attaining such an understanding include improving upon the current state-of-the-art sensor calibration and developing systematic validation methods for remotely sensed microphysical properties. While advances in active and passive remote sensors will lead to needed improvements in retrieval accuracies and capabilities, ongoing validation is essential so that the changing sensor characteristics do not mask atmospheric trends. Surface-based radiometer, chemical, and lidar networks have critical roles within an integrated observing system, yet they currently undersample key geographic regions, have limitations in certain measurement capabilities, and lack stable funding. In situ aircraft observations of size-resolved aerosol chemical composition are necessary to provide important linkages between active and passive remote sensing. A planned, systematic approach toward a global aerosol observing network, involving multiple sponsoring agencies and surface-based, suborbital, and spaceborne sensors, is required to prioritize trade-offs regarding capabilities and costs. This strategy is a key ingredient of the Progressive Aerosol Retrieval and Assimilation Global Observing Network (PARAGON) framework. A set of recommendations is presented.

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J. Boutin
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Y. Chao
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W. E. Asher
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T. Delcroix
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R. Drucker
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K. Drushka
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N. Kolodziejczyk
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T. Lee
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N. Reul
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G. Reverdin
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J. Schanze
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A. Soloviev
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L. Yu
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J. Anderson
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L. Brucker
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E. Dinnat
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A. Santos-Garcia
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W. L. Jones
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C. Maes
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T. Meissner
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W. Tang
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N. Vinogradova
, and
B. Ward

Abstract

Remote sensing of salinity using satellite-mounted microwave radiometers provides new perspectives for studying ocean dynamics and the global hydrological cycle. Calibration and validation of these measurements is challenging because satellite and in situ methods measure salinity differently. Microwave radiometers measure the salinity in the top few centimeters of the ocean, whereas most in situ observations are reported below a depth of a few meters. Additionally, satellites measure salinity as a spatial average over an area of about 100 × 100 km2. In contrast, in situ sensors provide pointwise measurements at the location of the sensor. Thus, the presence of vertical gradients in, and horizontal variability of, sea surface salinity complicates comparison of satellite and in situ measurements. This paper synthesizes present knowledge of the magnitude and the processes that contribute to the formation and evolution of vertical and horizontal variability in near-surface salinity. Rainfall, freshwater plumes, and evaporation can generate vertical gradients of salinity, and in some cases these gradients can be large enough to affect validation of satellite measurements. Similarly, mesoscale to submesoscale processes can lead to horizontal variability that can also affect comparisons of satellite data to in situ data. Comparisons between satellite and in situ salinity measurements must take into account both vertical stratification and horizontal variability.

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G. Vaughan
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J. Methven
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D. Anderson
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B. Antonescu
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L. Baker
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T. P. Baker
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S. P. Ballard
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K. N. Bower
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P. R. A. Brown
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J. Chagnon
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T. W. Choularton
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J. Chylik
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P. J. Connolly
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P. A. Cook
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R. J. Cotton
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J. Crosier
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C. Dearden
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J. R. Dorsey
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T. H. A. Frame
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M. W. Gallagher
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M. Goodliff
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S. L. Gray
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B. J. Harvey
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P. Knippertz
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H. W. Lean
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D. Li
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G. Lloyd
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O. Martínez–Alvarado
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J. Nicol
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J. Norris
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E. Öström
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J. Owen
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D. J. Parker
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R. S. Plant
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I. A. Renfrew
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N. M. Roberts
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P. Rosenberg
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A. C. Rudd
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D. M. Schultz
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J. P. Taylor
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T. Trzeciak
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R. Tubbs
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A. K. Vance
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P. J. van Leeuwen
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A. Wellpott
, and
A. Woolley

Abstract

The Diabatic Influences on Mesoscale Structures in Extratropical Storms (DIAMET) project aims to improve forecasts of high-impact weather in extratropical cyclones through field measurements, high-resolution numerical modeling, and improved design of ensemble forecasting and data assimilation systems. This article introduces DIAMET and presents some of the first results. Four field campaigns were conducted by the project, one of which, in late 2011, coincided with an exceptionally stormy period marked by an unusually strong, zonal North Atlantic jet stream and a succession of severe windstorms in northwest Europe. As a result, December 2011 had the highest monthly North Atlantic Oscillation index (2.52) of any December in the last 60 years. Detailed observations of several of these storms were gathered using the U.K.’s BAe 146 research aircraft and extensive ground-based measurements. As an example of the results obtained during the campaign, observations are presented of Extratropical Cyclone Friedhelm on 8 December 2011, when surface winds with gusts exceeding 30 m s–1 crossed central Scotland, leading to widespread disruption to transportation and electricity supply. Friedhelm deepened 44 hPa in 24 h and developed a pronounced bent-back front wrapping around the storm center. The strongest winds at 850 hPa and the surface occurred in the southern quadrant of the storm, and detailed measurements showed these to be most intense in clear air between bands of showers. High-resolution ensemble forecasts from the Met Office showed similar features, with the strongest winds aligned in linear swaths between the bands, suggesting that there is potential for improved skill in forecasts of damaging winds.

Open access
Theodore L. Anderson
,
Robert J. Charlson
,
Nicolas Bellouin
,
Olivier Boucher
,
Mian Chin
,
Sundar A. Christopher
,
Jim Haywood
,
Yoram J. Kaufman
,
Stefan Kinne
,
John A. Ogren
,
Lorraine A. Remer
,
Toshihiko Takemura
,
Didier Tanré
,
Omar Torres
,
Charles R. Trepte
,
Bruce A. Wielicki
,
David M. Winker
, and
Hongbin Yu

This document outlines a practical strategy for achieving an observationally based quantification of direct climate forcing by anthropogenic aerosols. The strategy involves a four-step program for shifting the current assumption-laden estimates to an increasingly empirical basis using satellite observations coordinated with suborbital remote and in situ measurements and with chemical transport models. Conceptually, the problem is framed as a need for complete global mapping of four parameters: clear-sky aerosol optical depth f f, radiative efficiency per unit optical depth δ, fine-mode fraction of optical depth f f, and the anthropogenic fraction of the fine mode f af . The first three parameters can be retrieved from satellites, but correlative, suborbital measurements are required for quantifying the aerosol properties that control E, for validating the retrieval of f f, and for partitioning fine-mode δ between natural and anthropogenic components. The satellite focus is on the “A-Train,” a constellation of six spacecraft that will fly in formation from about 2005 to 2008. Key satellite instruments for this report are the Moderate Resolution Imaging Spectroradiometer (MODIS) and Clouds and the Earth's Radiant Energy System (CERES) radiometers on Aqua, the Ozone Monitoring Instrument (OMI) radiometer on Aura, the Polarization and Directionality of Earth's Reflectances (POLDER) polarimeter on the Polarization and Anistropy of Reflectances for Atmospheric Sciences Coupled with Observations from a Lidar (PARASOL), and the Cloud and Aerosol Lider with Orthogonal Polarization (CALIOP) lidar on the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO). This strategy is offered as an initial framework—subject to improvement over time—for scientists around the world to participate in the A-Train opportunity. It is a specific implementation of the Progressive Aerosol Retrieval and Assimilation Global Observing Network (PARAGON) program, presented earlier in this journal, which identified the integration of diverse data as the central challenge to progress in quantifying global-scale aerosol effects. By designing a strategy around this need for integration, we develop recommendations for both satellite data interpretation and correlative suborbital activities that represent, in many respects, departures from current practice.

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Bruce A. Wielicki
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D. F. Young
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M. G. Mlynczak
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K. J. Thome
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S. Leroy
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J. Corliss
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J. G. Anderson
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C. O. Ao
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R. Bantges
,
F. Best
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K. Bowman
,
H. Brindley
,
J. J. Butler
,
W. Collins
,
J. A. Dykema
,
D. R. Doelling
,
D. R. Feldman
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N. Fox
,
X. Huang
,
R. Holz
,
Y. Huang
,
Z. Jin
,
D. Jennings
,
D. G. Johnson
,
K. Jucks
,
S. Kato
,
D. B. Kirk-Davidoff
,
R. Knuteson
,
G. Kopp
,
D. P. Kratz
,
X. Liu
,
C. Lukashin
,
A. J. Mannucci
,
N. Phojanamongkolkij
,
P. Pilewskie
,
V. Ramaswamy
,
H. Revercomb
,
J. Rice
,
Y. Roberts
,
C. M. Roithmayr
,
F. Rose
,
S. Sandford
,
E. L. Shirley
,
Sr. W. L. Smith
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B. Soden
,
P. W. Speth
,
W. Sun
,
P. C. Taylor
,
D. Tobin
, and
X. Xiong

The Climate Absolute Radiance and Refractivity Observatory (CLARREO) mission will provide a calibration laboratory in orbit for the purpose of accurately measuring and attributing climate change. CLARREO measurements establish new climate change benchmarks with high absolute radiometric accuracy and high statistical confidence across a wide range of essential climate variables. CLARREO's inherently high absolute accuracy will be verified and traceable on orbit to Système Internationale (SI) units. The benchmarks established by CLARREO will be critical for assessing changes in the Earth system and climate model predictive capabilities for decades into the future as society works to meet the challenge of optimizing strategies for mitigating and adapting to climate change. The CLARREO benchmarks are derived from measurements of the Earth's thermal infrared spectrum (5–50 μm), the spectrum of solar radiation reflected by the Earth and its atmosphere (320–2300 nm), and radio occultation refractivity from which accurate temperature profiles are derived. The mission has the ability to provide new spectral fingerprints of climate change, as well as to provide the first orbiting radiometer with accuracy sufficient to serve as the reference transfer standard for other space sensors, in essence serving as a “NIST [National Institute of Standards and Technology] in orbit.” CLARREO will greatly improve the accuracy and relevance of a wide range of space-borne instruments for decadal climate change. Finally, CLARREO has developed new metrics and methods for determining the accuracy requirements of climate observations for a wide range of climate variables and uncertainty sources. These methods should be useful for improving our understanding of observing requirements for most climate change observations.

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