  Multi-wavelength centimeter continuum observations of non-dusty,
non-pulsating K spectral-type red giants directly sample their chromospheres
and wind acceleration zones. Such stars are feeble emitters at these
wavelengths however, and previous observations have provided only a small
number of modest S/N measurements slowly accumulated over three decades. We
present multi-wavelength Karl G. Jansky Very Large Array thermal continuum
observations of the wind acceleration zones of two dust-free red giants,
Arcturus (Alpha Boo: K2 III) and Aldebaran (Alpha Tau: K5 III). Importantly,
most of our observations of each star were carried out over just a few days, so
that we obtained a snapshot of the different stellar atmospheric layers sampled
at different wavelengths, independent of any long-term variability. We report
the first detections at several wavelengths for each star including a detection
at 10 cm (3.0 GHz: S band) for both stars and a 20 cm (1.5 GHz: L band)
detection for Alpha Boo. This is the first time single luminosity class III red
giants have been detected at these continuum wavelengths. Our long-wavelength
data sample the outer layers of Alpha Boo's atmosphere where its wind velocity
is approaching its terminal value and the ionization balance is becoming
frozen-in. For Alpha Tau, however, our long-wavelength data are still sampling
its inner atmosphere, where the wind is still accelerating probably due to its
lower mass-loss rate. We compare our data with published semi-empirical models
based on ultraviolet data, and the marked deviations highlight the need for new
atmospheric models to be developed. Spectral indices are used to discuss the
possible properties of the stellar atmospheres, and we find evidence for a
rapidly cooling wind in the case of Alpha Boo. Finally, we develop a simple
analytical wind model for Alpha Boo based on our new long-wavelength flux
measurements.

Solar and Stellar Astrophysics