  In this manuscript, the temporal rainbow effect for surface acoustic waves
(SAW) is illustrated through a temporal analog of space metagradings. We show
that a time-modulated array of mechanical resonators induces a
wavenumber-preserving frequency transformation which, in turn, dictates
Rayleigh-to-Shear wave conversion. The process is unfolded through the
adiabatic theorem, which allows us to delineate the transition between a solely
frequency-converted wave packet and a temporally-driven mode conversion. In
other words, our paper explores the role of time modulation in the context of
elastic metasurfaces, and we envision our implementation to be suitable for
designing a new family of SAW devices with frequency conversion, mode
conversion, and unusual transport capabilities.
