Abstract
Abstract. Most atmospheric models, including the Weather Research and Forecasting (WRF) model, use a spherical geographic coordinate system to internally represent input data and perform computations. However, most geographic information system (GIS) input data used by the models are based on a spheroid datum because it better represents the actual geometry of the earth. WRF and other atmospheric models use these GIS input layers as if they were in a spherical coordinate system without accounting for the difference in datum. When GIS layers are not properly reprojected, latitudinal errors of up to 21 km in the midlatitudes are introduced. Recent studies have suggested that for very high-resolution applications, the difference in datum in the GIS input data (e.g., terrain land use, orography) should be taken into account. However, the magnitude of errors introduced by the difference in coordinate systems remains unclear. This research quantifies the effect of using a spherical vs. a spheroid datum for the input GIS layers used by WRF to study greenhouse gas transport and dispersion in northeast Pennsylvania.
Highlights
Geographic information science (GISc) datasets are usually projected on a spheroid geographic coordinate system (GCS) such as World Geodetic System 1984 (WGS84) or North American Datum 1983 (NAD83)
The GISc layers used as input data for the atmospheric models generally use a spheroid datum, but they are ingested by the models as if they used spherical datums
The GCS changes the spatial distribution of the terrain elevation, leading to these very large changes in wind direction The strong vertical gradients observed in the figure suggest there is a combination of influences from both the surface parameters, and the Coriolis components
Summary
Geographic information science (GISc) datasets are usually projected on a spheroid geographic coordinate system (GCS) such as World Geodetic System 1984 (WGS84) or North American Datum 1983 (NAD83). Atmospheric models are based on a spherical coordinate system because it usually leads to faster computations and easier representations of data (Monaghan et al, 2013). The GISc layers used as input data for the atmospheric models generally use a spheroid datum, but they are ingested by the models as if they used spherical datums. Using different GCSs can affect the model results because the input data are mapped to different locations. This difference can lead to latitudinal shifts up to 21 km in the midlatitudes (Monaghan et al, 2013). This paper performs a series of sensitivity studies where the GISs input layers are reprojected from a spheroid to a spherical datum in order to more correctly represent the input layers used by the atmospheric models
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