  We present the first detailed phase-resolved spectral analysis of a joint
Chandra High Energy Transmission Grating Spectrometer and Rossi X-ray Timing
Explorer observation of the rho variability class in the microquasar GRS
1915+105. The rho cycle displays a high-amplitude, double-peaked flare that
recurs roughly every 50 s, and is sometimes referred to as the "heartbeat"
oscillation. The spectral and timing properties of the oscillation are
consistent with the radiation pressure instability and the evolution of a local
Eddington limit in the inner disk. We exploit strong variations in the X-ray
continuum, iron emission lines, and the accretion disk wind to probe the
accretion geometry over nearly six orders of magnitude in distance from the
black hole. At small scales (1-10 R_g), we detect a burst of bremsstrahlung
emission that appears to occur when a portion of the inner accretion disk
evaporates due to radiation pressure. Jet activity, as inferred from the
appearance of a short X-ray hard state, seems to be limited to times near
minimum luminosity, with a duty cycle of ~10%. On larger scales (1e5-1e6 R_g)
we use detailed photoionization arguments to track the relationship between the
fast X-ray variability and the accretion disk wind. For the first time, we are
able to show that changes in the broadband X-ray spectrum produce changes in
the structure and density of the accretion disk wind on timescales as short as
5 seconds. These results clearly establish a causal link between the X-ray
oscillations and the disk wind and therefore support the existence of a
disk-jet-wind connection. Furthermore, our analysis shows that the mass loss
rate in the wind may be sufficient to cause long-term oscillations in the
accretion rate, leading to state transitions in GRS 1915+105.
