The computed precipitation over Greenland from the NCEP/NCAR and ECMWF reanalyses and from the omega-equation method (Chen et al. 1997) are contrasted with the observed accumulation, especially over the 180 km × 180 km region centered at Summit, Greenland. It is found that all of the computed precipitation rates are overly dry for this high elevation area, and that the topography of the Greenland Ice Sheet based on the modern data set of Ekholm (1996) has significant differences from that based on the U.S. Navy 10 arc minute global data set, which is used in all of the above computations. In order to check how the computed precipitation is affected by the topography, a comparison is presented between the precipitation amounts computed from the omega-equation method using these two different terrain data sets for Greenland.
Cyclones are primarily responsible for precipitation over Greenland, and heavy precipitation over the southern region is often related to lee cyclogenesis which is affected by the southern part of the Greenland Ice Sheet. The equivalent geopotential PHIe in sigma-coordinates used in the omega-equation method can also be applied to numerical models. A spectral limited-area model with the equivalent geopotential PHIe has been developed and used to simulate a lee cyclogenesis case near Greenland. A comparison of the cyclone development processes and precipitation between the model simulations with and without PHIe has been studied. How the cyclone development and precipitation are affected by the topography of the Greenland Ice Sheet is diagnosed.