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 \leavevmode \nobreak 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 } / \mathrm { dof } \sim 1 .
This reduction in RMS is partially driven by an improved standardization of Shallow Silicon and 91T-like SNe .

Conclusions :