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Gérald Desroziers, Loïk Berre, Vincent Chabot, and Bernard Chapnik

forecasts against radiosondes at 250 hPa, for North America and 20°–90°N domains. The scores are relatively neutral globally, although the impact is slightly positive during the 12–17 November period. This relative neutrality is related to the fact that observation and background error variances tend to be reduced here, by chance, by the same amount of tuning. An observed side effect of the reduction of both observation and background errors is that more observations are rejected, since a first part of

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Junjie Liu, Hong Li, Eugenia Kalnay, Eric J. Kostelich, and Istvan Szunyogh

humidity runs and the control run at the 300-hPa level. The statistically significant difference at the 95% level is about 5.0 m 2 s −2 for the error difference between the passive q and the control run, is 4.0 m 2 s −2 between the univariate q and the control run, and is 3.5 m 2 s −2 for the error difference between the multivariate q and the control run. The results ( Fig. 8 ) show that the difference is significant over most of the northern Pacific and the North America in the passive- q

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Seung-Jong Baek, Istvan Szunyogh, Brian R. Hunt, and Edward Ott

results. Bias model II is efficient in correcting the bias at locations where the observation density is high (e.g., over North America, Eurasia, and Australia in Fig. 10 ), while the hydrostatic-balance-based correction can correct a reasonably large portion of the bias at all locations where the difference between the model orography and the true orography is large ( Fig. 11 ). Combining the two bias-correction strategies, often leads to improvements which are larger than the sum of the

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Marc Bocquet

, H. , A. Strunk , H. Schmidt , and O. Talagrand , 2007 : Emission rate and chemical state estimation by 4-dimensional variational inversion. Atmos. Chem. Phys. , 7 , 3749 – 3769 . Fan , S-M. , M. Gloor , J. Mahlman , S. Pacala , J. L. Sarmiento , T. Takahashi , and P. P. Tans , 1998 : Atmospheric and oceanic CO 2 data and models imply a large terrestrial carbon sink in North America. Science , 282 , 442 – 444 . Fisher , M. , 2003 : Estimation of entropy

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