  Context. Observations of Type Ia supernovae (SNe Ia) can be used to derive
accurate cosmological distances through empirical standardization techniques.
Despite this success neither the progenitors of SNe Ia nor the explosion
process are fully understood. The U-band region has been less well observed for
nearby SNe, due to technical challenges, but is the most readily accessible
band for high-redshift SNe.
  Aims. Using spectrophotometry from the Nearby Supernova Factory, we study the
origin and extent of U-band spectroscopic variations in SNe Ia and explore
consequences for their standardization and the potential for providing new
insights into the explosion process.
  Methods. We divide the U-band spectrum into four wavelength regions
{\lambda}(uNi), {\lambda}(uTi), {\lambda}(uSi) and {\lambda}(uCa). Two of these
span the Ca H&K {\lambda}{\lambda} 3934, 3969 complex. We employ spectral
synthesis using SYNAPPS to associate the two bluer regions with Ni/Co and Ti.
  Results. (1) The flux of the uTi feature is an extremely sensitive
temperature/luminosity indicator, standardizing the SN peak luminosity to 0.116
$\pm$ 0.011 mag RMS. A traditional SALT2.4 fit on the same sample yields a
0.135 mag RMS. Standardization using uTi also reduces the difference in
corrected magnitude between SNe originating from different host galaxy
environments. (2) Early U-band spectra can be used to probe the Ni+Co
distribution in the ejecta, thus offering a rare window into the source of
lightcurve power. (3) The uCa flux further improves standardization, yielding a
0.086 $\pm$ 0.010 mag RMS without the need to include an additional intrinsic
dispersion to reach {\chi}$^2$/dof $\sim$ 1. This reduction in RMS is partially
driven by an improved standardization of Shallow Silicon and 91T-like SNe.
