SEARCH Projects

NOAA SEARCH Element 7: Initiation of an Arctic Reanalysis Activity in SEARCH

John Walsh David Bromwich Mark Serreze J. Tilley Institution: University of Alaska Fairbanks

Abstract

At the SEARCH Workshop on Large-Scale Atmosphere/Cryosphere Interactions (Seattle, WA, 27-29 November 2001), the presentations and discussions provided several reasons why a compelling case can be made for an Arctic reanalysis. First, the reanalysis would produce long time series of temporally and dynamically consistent fields (subject to changes in observing system input) of Arctic upper-air and surface winds, humidities and temperatures for studies of circulation variability (e.g., the AO, NAO and their Arctic manifestations); for budget studies; and for the driving of sea ice and ocean models. Second, the atmospheric component of the reanalysis would provide fields for which direct observations are sparse or problematic (e.g., precipitation, evapotranspiration, radiation and clouds) at higher spatial and temporal resolution, and with greater reliability, than from existing reanalyses. Third, the system-oriented approach required for a reanalysis would provide a community focus, involving at least the Arctic terrestrial, sea ice and atmospheric communities. Fourth, the reanalysis would leverage upon, and provide a synthesis of, Arctic field programs (SHEBA, LAII/ATLAS, ARM,…), capitalizing upon prior investments by bringing field results to bear upon the parameterizations used in large-scale models. Finally, the groundwork for an Arctic regional reanalysis can now be performed by capitalizing upon ongoing efforts such as ERA-40 and NCEP’s North American Regional Reanalysis (NARR), as well as recently compiled Polar Pathfinder products from satellites. The coincidence of this groundwork and the spin-up of SEARCH provides a unique window of opportunity for an Arctic reanalysis. However in addressing the viability of an Arctic system reanalysis, the recent workshop report1 notes that preliminary activities need to be undertaken now if SEARCH is to capitalize on this window of opportunity. For example, the reprocessing of the TOVS radiances will likely require several years. In addition, the momentum provided by ERA-40 and NCEP’s NARR can be harnessed for SEARCH only if the Arctic output from these efforts is evaluated by the Arctic community, allowing for the implementation of parameterizations tailored to Arctic conditions. The enhancement of ERA-40’s Arctic performance resulted from several years of such evaluation (and associated enhancements) of ERA-15 by a core of Arctic investigators, including M. Serreze and D. Bromwich of this project.