PNNL

Abstract

Nudging is a simulation technique widely used in the evaluation of atmospheric models and in sensitivity studies. The nudging strategy should be carefully selected so that it provides the desired constraint on the simulated atmospheric processes without introducing undue intervention. In this study, sensitivity experiments are conducted with the Energy Exascale Earth System Model (E3SM) Atmosphere Model version 1 (EAMv1) to identify setups that can give results representative of the model's long-term climate and meanwhile reasonably capture characteristics of the observed meteorological conditions to facilitate the comparison of model results with measurements. We show that when the prescribed meteorological conditions are temporally interpolated to the model time and used to constrain EAM’s horizontal winds at each time step, a nudged simulation can reproduce the characteristic evolution of the observed weather events (especially in mid- and high latitudes) as well as the model's long-term climatology, although nudging also leads to non-negligible regional changes in wind-driven aerosol emissions, low-level clouds, and cloud/precipitation near the maritime continent. Compared to its predecessor model used in an earlier study, EAMv1 is less sensitive to temperature nudging, although temperature nudging still has significant impact on the simulated cloud radiative effects. EAMv1 remains very sensitive to humidity nudging. Constraining humidity substantially improves the correlation for tropical precipitation, but also leads to large changes in the long-term statistics of precipitation, clouds, and aerosol lifecycle. Humidity and temperature nudging should be used with care but might provide important hints on further improvement of the EAM model.