author = "Mesinger, Fedor and Veljovic, Katarina",
          affiliation = "{Instituto Nacional de Pesquisas Espaciais (INPE)} and {University 
                         of Belgrade}",
                title = "Eta vs. sigma: review of past results, Gallus–Klemp test, and 
                         large-scale wind skill in ensemble experiments",
              journal = "Meteorology and Atmospheric Physics",
                 year = "2017",
               volume = "129",
               number = "9",
                pages = "573--593",
                month = "Dec.",
             abstract = "To determine the effect of switching between the eta and the sigma 
                         coordinate in numerical weather prediction involving topography, 
                         five sets of tests were performed. The eta version did better in 
                         all of them particularly with precipitation scores and more 
                         accurate placement of storms. However, a problem of flow 
                         separation in the lee of the bell-shaped topography discovered by 
                         Gallus and Klemp seemed to many to suggest the eta coordinate to 
                         be ill suited for high-resolution models. Flow separation is shown 
                         not to occur following a refinement of the eta discretization. 
                         Trying to identify a primary cause of the improvement in 250 hPa 
                         winds previously demonstrated in Eta ensemble members over their 
                         ECMWF driver members, ten of the Eta members were run switched to 
                         sigma. At a critical time, the Eta members in eta mode showed a 
                         tendency for more accurate tilt of a 250 hPa trough than the 
                         members run in sigma mode. The experiment was rerun for a more 
                         recent and higher resolution ECMWF ensemble, and for an increased 
                         number of members. The advantage of the Eta over ECMWF is seen 
                         again, even though this time, the Eta resolution during the first 
                         10 days of the experiment was about the same as that of driver 
                         members. Rerunning the Eta ensemble switched to sigma showed an 
                         advantage in the Eta/eta 250 hPa wind scores used, again 
                         associated with an upper-air trough's movement across the Rockies. 
                         Better positioning of lee lows ahead of these troughs using 
                         Eta/eta is suggested to be making significant contributions to its 
                         better precipitation scores. Implications of experiments done for 
                         regional climate modeling are discussed as well.",
                  doi = "10.1007/s00703-016-0496-3",
                  url = "http://dx.doi.org/10.1007/s00703-016-0496-3",
                 issn = "0177-7971",
             language = "en",
           targetfile = "fedor_eta.pdf",
        urlaccessdate = "29 nov. 2020"