  Neustadt & Kochanek (2022, hereafter NK22) proposed a new method to
reconstruct the temperature perturbation map (as functions of time and disc
radius) of AGN accretion discs using multi-wavelength photometric light curves.
We apply their technique to 100 quasars at $z=0.5-2$ from the Sloan Digital Sky
Survey Reverberation Mapping project, using multi-epoch spectroscopy that
covers rest-frame UV-optical continuum emission from the quasar and probes days
to months timescales. Consistent with NK22 for low-redshift AGNs, we find that
the dominant pattern of disc temperature perturbations is either slow
inward/outward moving waves with typical amplitudes $\delta T/T_0\sim 10\%$
traveling at $\sim 0.01-0.1c$, with a typical radial frequency of $\sim$ 0.5
dex in $\log R$, or incoherent perturbations. In nearly none of the cases do we
find clear evidence for coherent, fast outgoing temperature perturbations at
the speed of light, reminiscent of the lamppost model; but such lamppost
signals may be present in some quasars for limited periods of the monitoring
data. Using simulated data, we demonstrate that high-fidelity temperature
perturbation maps can be recovered with high-quality monitoring spectroscopy,
with limited impact from seasonal gaps in the data. On the other hand,
reasonable temperature perturbation maps can be reconstructed with high-cadence
photometric light curves from the Vera C. Rubin Observatory Legacy Survey of
Space and Time. Our findings, together with NK22, suggest that internal disc
processes are the main driver for temperature fluctuations in AGN accretion
discs over days to months timescales.
