  A linear response function (LRF) determines the mean-response of a nonlinear
climate system to weak imposed forcings, and an eddy flux matrix (EFM)
determines the eddy momentum and heat flux responses to mean-flow changes.
Neither LRF nor EFM can be calculated from first principles due the lack of a
complete theory for turbulent eddies. Here the LRF and EFM for an idealized dry
atmosphere are computed by applying numerous localized weak forcings, one at a
time, to a GCM with Held-Suarez physics and calculating the mean-responses. The
LRF and EFM for zonally-averaged responses are then constructed using these
forcings and responses through matrix inversion. Tests demonstrate that LRF and
EFM are fairly accurate. Spectral analysis of the LRF shows that the most
excitable dynamical mode, the neutral vector, strongly resembles the model's
Annular Mode. The framework described here can be employed to compute the
LRF/EFM for zonally-asymmetric responses and more complex GCMs. The potential
applications of the LRF/EFM constructed here are i) forcing a specified
mean-flow for hypothesis-testing, ii) isolating/quantifying the eddy-feedbacks
in complex eddy-mean flow interaction problems, and iii) evaluating/improving
more generally-applicable methods currently used to construct LRFs or diagnose
eddy-feedbacks in comprehensive GCMs or observations. As an example for iii, in
Part 2, the LRF is also computed using the fluctuation-dissipation theorem
(FDT), and the previously-calculated LRF is exploited to investigate why FDT
performs poorly in some cases. It is shown that dimension-reduction using
leading EOFs, which is commonly used to construct LRFs from the FDT, can
significantly degrade the accuracy due to the non-normality of the operator.
