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D. J. Lea, I. Mirouze, M. J. Martin, R. R. King, A. Hines, D. Walters, and M. Thurlow

Abstract

A new coupled data assimilation (DA) system developed with the aim of improving the initialization of coupled forecasts for various time ranges from short range out to seasonal is introduced. The implementation here is based on a “weakly” coupled data assimilation approach whereby the coupled model is used to provide background information for separate ocean–sea ice and atmosphere–land analyses. The increments generated from these separate analyses are then added back into the coupled model. This is different from the existing Met Office system for initializing coupled forecasts, which uses ocean and atmosphere analyses that have been generated independently using the FOAM ocean data assimilation system and NWP atmosphere assimilation systems, respectively. A set of trials has been run to investigate the impact of the weakly coupled data assimilation on the analysis, and on the coupled forecast skill out to 5–10 days. The analyses and forecasts have been assessed by comparing them to observations and by examining differences in the model fields. Encouragingly for this new system, both ocean and atmospheric assessments show the analyses and coupled forecasts produced using coupled DA to be very similar to those produced using separate ocean–atmosphere data assimilation. This work has the benefit of highlighting some aspects on which to focus to improve the coupled DA results. In particular, improving the modeling and data assimilation of the diurnal SST variation and the river runoff should be examined.

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D. L. Westphal, T. R. Holt, S. W. Chang, N. L. Baker, T. F. Hogan, L. R. Brody, R. A. Godfrey, J. S. Goerss, J. A. Cummings, D. J. Laws, and C. W. Hines

Abstract

The Marine Meteorology Division of the Naval Research Laboratory (NRL), assisted by the Fleet Numerical Meteorology and Oceanography Center, has performed global and mesoscale reanalyses to support the study of Gulf War illness. Realistic and quantitatively accurate atmospheric conditions are needed to drive dispersion models that can predict the transport and dispersion of chemical agents that may have affected U.S. and other coalition troops in the hours and days following the demolition of chemical weapons at Khamisiyah, Iraq, at approximately 1315 UTC 10 March 1991. The reanalysis was conducted with the navy’s global and mesoscale analysis and prediction systems: the Navy Operational Global Atmospheric Prediction System and the NRL Coupled Ocean–Atmosphere Mesoscale Prediction System. A comprehensive set of observations has been collected and used in the reanalysis, including unclassified and declassified surface reports, ship and buoy reports, observations from pibal and rawinsonde, and retrievals from civilian and military satellites. The atmospheric conditions for the entire globe have been reconstructed using the global system at the effective spatial resolution of 0.75°. The atmospheric conditions over southern Iraq, Kuwait, and northern Saudi Arabia have been reconstructed using the mesoscale system at the spatial resolutions of 45, 15, and 5 km. In addition to a baseline reanalysis, perturbation analyses were also performed to estimate the atmospheric sensitivity to observational error and analysis error. The results suggest that the reanalysis has bounded the variability and that the actual atmospheric conditions were unlikely to differ significantly from the reanalysis.

The synoptic conditions at and after the time of the detonation were typical of the transitional period after a Shamal and controlled by eastward-propagating small-amplitude troughs and ridges. On the mesoscale, the conditions over the Tigris–Euphrates Valley were further modulated by the diurnal variation in the local circulations between land, the Persian Gulf, and the Zagros Mountains. The boundary layer winds at Khamisiyah were from NNW at the time of the detonation and shifted to WNW in the nocturnal boundary layer. On the second day, a strong high passed north of Khamisiyah and the winds strengthened and turned to the ESE. During the third day, the region was dominated by the approach and passage of a low pressure system and the associated front with the SE winds veering to NW.

A transport model for passive scalars was used to illustrate the sensitivity to the reanalyzed fields of potential areas of contamination. Transport calculations based on various release scenario and reanalyzed meteorological conditions suggest that the mean path of the released chemical agents was southward from Khamisiyah initially, turning westward, and eventually northwestward during the 72-h period after the demolition. Precipitation amounts in the study area were negligible and unlikely to have an effect on the nerve agent.

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D. H. Bromwich, A. B. Wilson, L. Bai, Z. Liu, M. Barlage, C.-F. Shih, S. Maldonado, K. M. Hines, S.-H. Wang, J. Woollen, B. Kuo, H.-C. Lin, T.-K. Wee, M. C. Serreze, and J. E. Walsh

Abstract

The Arctic is a vital component of the global climate, and its rapid environmental evolution is an important element of climate change around the world. To detect and diagnose the changes occurring to the coupled Arctic climate system, a state-of-the-art synthesis for assessment and monitoring is imperative. This paper presents the Arctic System Reanalysis, version 2 (ASRv2), a multiagency, university-led retrospective analysis (reanalysis) of the greater Arctic region using blends of the polar-optimized version of the Weather Research and Forecasting (Polar WRF) Model and WRF three-dimensional variational data assimilated observations for a comprehensive integration of the regional climate of the Arctic for 2000–12. New features in ASRv2 compared to version 1 (ASRv1) include 1) higher-resolution depiction in space (15-km horizontal resolution), 2) updated model physics including subgrid-scale cloud fraction interaction with radiation, and 3) a dual outer-loop routine for more accurate data assimilation. ASRv2 surface and pressure-level products are available at 3-hourly and monthly mean time scales at the National Center for Atmospheric Research (NCAR). Analysis of ASRv2 reveals superior reproduction of near-surface and tropospheric variables. Broadscale analysis of forecast precipitation and site-specific comparisons of downward radiative fluxes demonstrate significant improvement over ASRv1. The high-resolution topography and land surface, including weekly updated vegetation and realistic sea ice fraction, sea ice thickness, and snow-cover depth on sea ice, resolve finescale processes such as topographically forced winds. Thus, ASRv2 permits a reconstruction of the rapid change in the Arctic since the beginning of the twenty-first century–complementing global reanalyses. ASRv2 products will be useful for environmental models, verification of regional processes, or siting of future observation networks.

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William L. Smith Jr., Christy Hansen, Anthony Bucholtz, Bruce E. Anderson, Matthew Beckley, Joseph G. Corbett, Richard I. Cullather, Keith M. Hines, Michelle Hofton, Seiji Kato, Dan Lubin, Richard H. Moore, Michal Segal Rosenhaimer, Jens Redemann, Sebastian Schmidt, Ryan Scott, Shi Song, John D. Barrick, J. Bryan Blair, David H. Bromwich, Colleen Brooks, Gao Chen, Helen Cornejo, Chelsea A. Corr, Seung-Hee Ham, A. Scott Kittelman, Scott Knappmiller, Samuel LeBlanc, Norman G. Loeb, Colin Miller, Louis Nguyen, Rabindra Palikonda, David Rabine, Elizabeth A. Reid, Jacqueline A. Richter-Menge, Peter Pilewskie, Yohei Shinozuka, Douglas Spangenberg, Paul Stackhouse, Patrick Taylor, K. Lee Thornhill, David van Gilst, and Edward Winstead

Abstract

The National Aeronautics and Space Administration (NASA)’s Arctic Radiation-IceBridge Sea and Ice Experiment (ARISE) acquired unique aircraft data on atmospheric radiation and sea ice properties during the critical late summer to autumn sea ice minimum and commencement of refreezing. The C-130 aircraft flew 15 missions over the Beaufort Sea between 4 and 24 September 2014. ARISE deployed a shortwave and longwave broadband radiometer (BBR) system from the Naval Research Laboratory; a Solar Spectral Flux Radiometer (SSFR) from the University of Colorado Boulder; the Spectrometer for Sky-Scanning, Sun-Tracking Atmospheric Research (4STAR) from the NASA Ames Research Center; cloud microprobes from the NASA Langley Research Center; and the Land, Vegetation and Ice Sensor (LVIS) laser altimeter system from the NASA Goddard Space Flight Center. These instruments sampled the radiant energy exchange between clouds and a variety of sea ice scenarios, including prior to and after refreezing began. The most critical and unique aspect of ARISE mission planning was to coordinate the flight tracks with NASA Cloud and the Earth’s Radiant Energy System (CERES) satellite sensor observations in such a way that satellite sensor angular dependence models and derived top-of-atmosphere fluxes could be validated against the aircraft data over large gridbox domains of order 100–200 km. This was accomplished over open ocean, over the marginal ice zone (MIZ), and over a region of heavy sea ice concentration, in cloudy and clear skies. ARISE data will be valuable to the community for providing better interpretation of satellite energy budget measurements in the Arctic and for process studies involving ice–cloud–atmosphere energy exchange during the sea ice transition period.

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