  When utilizing the NIRISS/SOSS mode on JWST, the pupil wheel (tasked with
orienting the GR700XD grism into the optical path) does not consistently settle
into its commanded position resulting in a minor misalignment with deviations
of a few fractions of a degree. These small offsets subsequently introduce
noticeable changes in the trace positions of the NIRISS SOSS spectral orders
between visits. This inconsistency, in turn, can lead to variations of the
wavelength solution. In this report, we present the visit-to-visit
characterization of the NIRISS GR700XD Wavelength Calibration for spectral
orders 1 and 2. Employing data from Calibration Program 1512 (PI: Espinoza),
which intentionally and randomly sampled assorted pupil wheel positions during
observations of the A-star BD+60-1753, as well as data from preceding
commissioning and calibration activities to model this effect, we demonstrate
that the wavelength solution can fluctuate in a predictable fashion between
visits by up to a few pixels. We show that via two independent polynomial
regression models for spectral orders 1 and 2, respectively, using the measured
x-pixel positions of known Hydrogen absorption features in the A-star spectra
and pupil wheel positions as regressors, we can accurately predict the
wavelength solution for a particular visit with an RMS error within a few
tenths of a pixel. We incorporate these models in PASTASOSS, a Python package
for predicting the GR700XD spectral traces, which now allows to accurately
predict spectral trace positions and their associated wavelengths for any
NIRISS/SOSS observation.
