Orography --------- From "Model": Raw orography obtained from the U.S. Navy dataset with resolution of 10 minutes arc (cf. Joseph 1980) is area-averaged on the T62 Gaussian grid of the NCEP operational model. Orographic variances also are computed on the T62 Gaussian grid for use in the gravity-wave drag parameterization (see Gravity-wave Drag). Joseph, D., 1980: Navy 10' global elevation values. National Center for Atmospheric Research notes on the FNWC terrain data set, 3 pp. Comments: (11/2000) 1) The "area averaged T62 Gaussian grid orography" was transformed into T62 spectral space and back onto the T62 grid for use by the model. This set of transformations introduced "Gibb-ing". (The Gibb's phenomena is caused by the number of degrees of freedom in the T62 Gaussian (quadratic) grid being larger than in the spectral representation). As a result, sharp gradients in orography tend to have over-shoots or ringing. For example, off the coast of Peru, the Pacific ocean is hundreds of meters below sea level. Similarly Denmark and parts of Asia are below sea level. "Gibb-ing" can be reduced by using smoothed orography (at the expense of increasing the RMS error) and by increasing the resolution of the analyses (making some assumptions about the orography). 2) The global orography used by NCEP has been updated. Major differences were found in Asia and Antarctica. No experiments have been made to study the impact of the new orography on the (relatively low resolution) T62 model.