Journal Article

Impact of Nudging Strategy on the Climate Representativeness and Hindcast Skill of Constrained EAMv1 Simulations

Ma, Po‐Lun, Zhang, Shixuan, Tang, Qi, Sun, Jian, Zhang, Kai, Wan, Hui

2019

Overview

Nudging is a simulation technique widely used in sensitivity studies and in the evaluation of atmosphere models. Care is needed in the experimental setup in order to achieve 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 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 middle and high latitudes) as well as the model's long‐term climatology, although nudging also leads to nonnegligible regional changes in wind‐driven aerosol emissions, low‐level clouds in the stratocumulus regime, and cloud and precipitation near the maritime continent. Compared to its predecessor model used in an earlier study, EAMv1 is less sensitive to temperature nudging, although significant impacts on the cloud radiative effects still exist. EAMv1 remains very sensitive to humidity nudging. Constraining humidity substantially improves the correlation between the simulated and observed tropical precipitation but also leads to large changes in the long‐term statistics of the simulated precipitation, clouds, and aerosol lifecycle. Plain Language Summary For the development and application of numerical weather and climate models, it is often useful to constrain a numerical experiment so that the evolution of the meteorological conditions follows a specific pathway. One of the techniques to apply such constraints is nudging, which introduces additional terms to the model equations. This study performs and analyzes sensitivity experiments with an attempt to identify implementations of nudging that can provide sufficient constraints without severely interfering with the simulations. Key Points EAMv1 with continuous nudging captures synoptic events very well in middle and high latitudes but less well in the tropics Nudging T or Q in addition to horizontal winds improves the correlation but leads to significant changes in the long‐term climate Wind‐driven aerosol emissions, stratocumulus clouds, and clouds/precipitation near the maritime continent are sensitive to wind nudging

• Publisher: John Wiley & Sons, Inc,American Geophysical Union (AGU)
• Subject: Aerosols / Atmosphere / Atmospheric models / Atmospheric processes / Climate / Climate models / Climatology / Clouds / E3SM / EAMv1 / Earth / ENVIRONMENTAL SCIENCES / Experiments / General circulation models / hindcast / Humidity / Meteorological conditions / Meteorology / nudging / Physics / Precipitation / Simulation / Statistical methods / Stratocumulus clouds / Tropical climate / Winds