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The singular value decomposition of the mean-flow-based resolvent operator,or resolvent analysis, has proven to provide essential insights into thedynamics of various turbulent flows. In this study, we perform a resolventanalysis of a compressible turbulent jet, where the optimisation domain of theresponse modes is located in the acoustic field, excluding the hydrodynamicregion, in order to promote acoustically efficient modes. We examine theproperties of the acoustic resolvent and assess its potential for jet-noisemodelling, focusing on the subsonic regime. We compare resolvent modes withSPOD modes educed from LES data. Resolvent forcing modes, consistent withprevious studies, are found to contain supersonic waves associated with Machwave radiation in the response modes. This differs from the standard resolventin which hydrodynamic instabilities dominate. Acoustic resolvent response modesgenerally have better alignment with acoustic SPOD modes than standardresolvent response modes. For the optimal mode, the angle of the acoustic beamis close to that found in SPOD modes for moderate frequencies. However, thereis no significant separation between the singular values of the leading andsub-optimal modes. Some suboptimal modes are furthermore shown to containirrelevant structure for jet noise. Thus, even though it contains essentialacoustic features absent from the standard resolvent approach, the SVD of theacoustic resolvent alone is insufficient to educe a low-rank model for jetnoise. But because it identifies the prevailing mechanisms of jet noise, itprovides valuable guidelines in the search of a forcing model (Karban$\textit{et al.}$ 2022, An empirical model of noise sources in subsonic jets.arXiv preprint arXiv:2210.01866).

Resolvent modelling of jet noise: the need for forcing models