  We report on our observing program to capture simultaneous spectra of Ca II
and Balmer lines in a sample of nearby M3 dwarfs. Our goal is to investigate
the chromospheric temperature structure required to produce these lines at the
observed levels. We find a strong positive correlation between instantaneous
measurements of Ca II K and the Balmer lines in active stars, although these
lines may not be positively correlated in time-resolved measurements. The
relationship between H alpha and Ca II K remains ambiguous for weak and
intermediate activity stars, with H alpha absorption corresponding to a range
of Ca II K emission. A similar relationship is also observed between Ca II K
and the higher order Balmer lines. As our sample consists of a single spectral
type, correlations between these important chromospheric tracers cannot be
ascribed to continuum effects, as suggested by other authors. These data
confirm prior non-simultaneous observations of the H alpha line behavior with
increasing activity, showing an initial increase in the H alpha absorption with
increasing Ca II K emission, prior to H alpha filling in and eventually
becoming a pure emission line in the most active stars. We also compare our
optical measurements with archival UV and X-ray measurements, finding a
positive correlation between the chromospheric and coronal emission for both
high and intermediate activity stars. We compare our results with previous
determinations of the active fraction of low mass stars, and discuss them in
the context of surface inhomogeneity. Lastly, we discuss the application of
these data as empirical constraints on new static models of quiescent M dwarf
atmospheres.
