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Ludovic Auger and Andrew V. Tangborn

Abstract

A suboptimal Kalman filter system that evolves error covariances in terms of a truncated set of wavelet coefficients has been developed for the assimilation of chemical tracer observations of CH4. The truncation is carried out in such a way that the resolution of the error covariance is reduced only in the zonal direction, where gradients are smaller. Assimilation experiments, which lasted 24 days and used different degrees of truncation, were carried out. These experiments reduced the number of elements in the covariance matrix by 90%, 97%, and 99% and the computational cost of covariance propagation by 80%, 93%, and 96%, respectively. The difference in both error covariance and the tracer field between the truncated and full systems over this period was not found to be growing after about 5 days of assimilation. The largest errors in the tracer fields were found to occur in regions of largest zonal gradients at times when observations were made in the immediate vicinity.

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Andrew Tangborn, Robert Cooper, Steven Pawson, and Zhibin Sun

Abstract

A source inversion technique for chemical constituents is presented that uses assimilated constituent observations rather than directly using the observations. The method is tested with a simple model problem, which is a two-dimensional Fourier–Galerkin transport model combined with a Kalman filter for data assimilation. Inversion is carried out using a Green’s function method and observations are simulated from a true state with added Gaussian noise. The forecast state uses the same spectral model but differs by an unbiased Gaussian model error and emissions models with constant errors. The numerical experiments employ both simulated in situ and satellite observation networks. Source inversion was carried out either by directly using synthetically generated observations with added noise or by first assimilating the observations and using the analyses to extract observations. Twenty identical twin experiments were conducted for each set of source and observation configurations, and it was found that in the limiting cases of a very few localized observations or an extremely large observation network there is little advantage to carrying out assimilation first. For intermediate observation densities, the source inversion error standard deviation is decreased by 50% to 90% when the observations are assimilated with the Kalman filter before carrying out the Green’s function inversion.

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Sergio De Souza-Machado, Andrew Tangborn, Philip Sura, Christopher Hepplewhite, and L. Larrabee Strow

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Statistical relationships between higher-order moments of probability density functions (PDFs) are used to analyze top-of-atmosphere radiance measurements made by the Atmospheric Infrared Sounder (AIRS) and radiance calculations from the ECMWF Re-Analysis (ERA) and the Modern-Era Retrospective Analysis for Research and Applications (MERRA) over a 10-yr period. The statistical analysis used in this paper has previously been applied to sea surface temperature, and here the authors show that direct satellite radiance observations of atmospheric variability also exhibit stochastic forcing characteristics. The authors have chosen six different AIRS channels based on the sensitivity of their measured radiances to a variety of geophysical properties. In each of these channels, the authors have found evidence of correlated additive and multiplicative (CAM) stochastic forcing. In general, channels sensitive to tropospheric humidity and surface temperature show the strongest evidence of CAM forcing, while those sensitive to stratospheric temperature and ozone exhibit the weakest forcing. Radiance calculations from ERA and MERRA agree well with AIRS measurements in the Gaussian part of the PDFs but show some differences in the tails, indicating that the reanalyses may be missing some extrema there. The CAM forcing is investigated through numerical simulation of simple stochastic differential equations (SDEs). The authors show how measurements agree better with weaker CAM forcing, achieved by reducing the multiplicative forcing or by increasing the spatial correlation of the added noise in the case of an SDE with one spatial dimension. This indicates that atmospheric models could be improved by adjusting nonlinear terms that couple long and short time scales.

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Florence Rabier, Aurélie Bouchard, Eric Brun, Alexis Doerenbecher, Stéphanie Guedj, Vincent Guidard, Fatima Karbou, Vincent-Henri Peuch, Laaziz El Amraoui, Dominique Puech, Christophe Genthon, Ghislain Picard, Michael Town, Albert Hertzog, François Vial, Philippe Cocquerez, Stephen A. Cohn, Terry Hock, Jack Fox, Hal Cole, David Parsons, Jordan Powers, Keith Romberg, Joseph VanAndel, Terry Deshler, Jennifer Mercer, Jennifer S. Haase, Linnea Avallone, Lars Kalnajs, C. Roberto Mechoso, Andrew Tangborn, Andrea Pellegrini, Yves Frenot, Jean-Noël Thépaut, Anthony McNally, Gianpaolo Balsamo, and Peter Steinle

The Concordiasi project is making innovative observations of the atmosphere above Antarctica. The most important goals of the Concordiasi are as follows:

  • To enhance the accuracy of weather prediction and climate records in Antarctica through the assimilation of in situ and satellite data, with an emphasis on data provided by hyperspectral infrared sounders. The focus is on clouds, precipitation, and the mass budget of the ice sheets. The improvements in dynamical model analyses and forecasts will be used in chemical-transport models that describe the links between the polar vortex dynamics and ozone depletion, and to advance the under understanding of the Earth system by examining the interactions between Antarctica and lower latitudes.

  • To improve our understanding of microphysical and dynamical processes controlling the polar ozone, by providing the first quasi-Lagrangian observations of stratospheric ozone and particles, in addition to an improved characterization of the 3D polar vortex dynamics. Techniques for assimilating these Lagrangian observations are being developed.

A major Concordiasi component is a field experiment during the austral springs of 2008–10. The field activities in 2010 are based on a constellation of up to 18 long-duration stratospheric super-pressure balloons (SPBs) deployed from the McMurdo station. Six of these balloons will carry GPS receivers and in situ instruments measuring temperature, pressure, ozone, and particles. Twelve of the balloons will release dropsondes on demand for measuring atmospheric parameters. Lastly, radiosounding measurements are collected at various sites, including the Concordia station.

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Florence Rabier, Steve Cohn, Philippe Cocquerez, Albert Hertzog, Linnea Avallone, Terry Deshler, Jennifer Haase, Terry Hock, Alexis Doerenbecher, Junhong Wang, Vincent Guidard, Jean-Noël Thépaut, Rolf Langland, Andrew Tangborn, Gianpaolo Balsamo, Eric Brun, David Parsons, Jérôme Bordereau, Carla Cardinali, François Danis, Jean-Pierre Escarnot, Nadia Fourrié, Ron Gelaro, Christophe Genthon, Kayo Ide, Lars Kalnajs, Charlie Martin, Louis-François Meunier, Jean-Marc Nicot, Tuuli Perttula, Nicholas Potts, Patrick Ragazzo, David Richardson, Sergio Sosa-Sesma, and André Vargas
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