The monthly surface pressure layer is an assimilated data from NASA second Modern-Era Retrospective analysis for Research and Applications (MERRA-2), produced by the Goddard Earth Observing System Model, Version 5 (GEOS-5) data assimilation system. The layer’s units are in hectopascals (hPa). The monthly surface pressure is time aggregated from corresponding 3-hourly data with spatial resolution of 0.625° × 0.5°.

This parameter (PS) was extracted from the product M2IMNPASM.5.12.4 (Monthly mean, Instantaneous, Pressure-Level, Assimilation, Assimilated Meteorological Fields).

References: Modern-Era Retrospective analysis for Research and Applications, Version 2 Documentation