Data Assimilation in the Ocean and in the Atmosphere : What Should be Next? (gtSpecial IssueltData Assimilation in Meteology and Oceanography: Theory and Practice)

摘要

As part of the International Symposium on Assimilation of Observations in Meteorology and Oceanography, a panel discussion was held on the O1997, Meteorological Society of Japan evening of 15 March 1995. The purpose of this panel discussion was to focus on what the next major areas of research in data assimilation should be. The panelists had five minutes each for short presentations and this was followed by an open discussion. The Appendix summarizes the opinions of the panelists, and of a few additional well-known practitioners of data assimilation, on major areas requiring development in the future. Several themes emerged repeatedly among the individual statements (see also "Open questions" in Ghil, 1997): 1) the need to include "errors of the day" in data assimilation of unstable systems such as the atmosphere, and perhaps the coupled ocean-atmosphere (Anderson, Cohn, Courtier, Kalnay, Parrish, Purser); 2) the need to perform observational impact studies to determine the most cost-effective observing systems (Busalacchi, Schlatter); 3) the need to improve the models to ensure that they have attractors not too different from nature (Bennett, Busalacchi, Parrish). The statement "the principal influence of the assimilated data (in tropical ocean data assimilation) is to eliminate systematic biases in the model temperature fields" (Busalacchi, 1996) would suggest that the improvement of the ocean models is, at this time, more important than any assimilation technique. For the coupled models it is of paramount importance that the ocean forcings (e.g., wind Stress) also be close to the real forcings (Anderson); 4) the need to tackle new areas of data assimilation (mesoscale, land surface, coupled ocean atmosphere) (Anderson, Sato, Schlatter), and new types of observations (Derber); 5) the need to develop advanced data assimilation systems which are computationally affordable (Cohn, Lorenc); 6) the need to estimate analysis errors and to test the validity of these estimates with data (Bennett, Busalacchi, Cohn, Purser); 7) the need for methods that do not smear small-scale structures (Bennett, Purser). During the discussion, several additional points were brought up: Prof. Y. Sasaki (U. Oklahoma) showed how new observing systems (such as NEXRAD) allow the possibility of data assimilation for such small-scale phenomena as microbursts. G.Evensen (NERSC, Norway) asked what could be the role of data assimilation in small countries. One answer offered by J. Cramm (Forecast Systems Lab-oratory, NOAA): a local-area analysis and predication system (like NCEP's LAPS). E. Brin (Goddard, NASA) asked whether it was possible to use reanalyses for studies of climate change. Answer by A. Lorenc (UKMO): basically no. (One exception is the use of optimal averaging within the reanalysis processing, which improves the estimate of the areal average from the observations, and provides an estimate of its error).