annular mode in an idealized GCM. This provides the “ground truth" in the idealized GCM, and serves as a benchmark against which one can assess the statistical methods. The LRF will be briefly explained in Section 2, along with model configuration and the reanalysis data. In Section 3, the annular mode and a simple model of eddy-jet feedback will be introduced, followed by quantification of the feedback strength using different methods in Section 4. Discussions and a brief summary are presented in Section 5.

Methodology
===========

For the numerical simulations, we use the Geophysical Fluid Dynamics Laboratory dry dynamical core, which solves the primitive equations with Held-Suarez forcing [@Held1994]. Temperature is relaxed to an equinoctial radiative-equilibrium state with an equator-to-pole temperature difference of 60 K. Similar setups have been widely used to study the midlatitude circulation and its low-frequency variability [e.g., @Gerber2008b; @Chen2009; @Hassanzadeh2014; @Hassanzadeh2015; @McGraw2016]. Each simulation is integrated for 45000 days at the T63 resolution (horizontal spacing of around 200 km) with 40 vertical levels and 6-hourly outputs, and the first 500 days are discarded. Ten ensemble simulations are conducted for the control (CTL) and an experiment (EXP). In EXP, a zonally symmetric time-invariant forcing is applied to 