  Atmospheric compositions offer valuable clues to planetary formation and
evolution. Jupiter has been the most well-studied giant planet in terms of its
atmosphere; however, the origin of the Jovian atmospheric composition remains a
puzzle as the abundances of nitrogen and noble gases as high as those of other
elements could only originate from extremely cold environments. We propose a
novel idea for explaining the Jovian atmospheric composition: Dust pileup at
the H$_2$O snow line casts a shadow and cools the Jupiter orbit so that N$_2$
and noble gases can freeze. Planetesimals or a core formed in the shadowed
region can enrich nitrogen and noble gases as much as other elements through
their dissolution in the envelope. We compute the temperature structure of a
shadowed protosolar disk with radiative transfer calculations. Then, we
investigate the radial volatile distributions and predict the atmospheric
composition of Jupiter with condensation calculations. We find that the
vicinity of the current Jupiter orbit, approximately $3$--$7~{\rm AU}$, could
be as cold as $30~{\rm K}$ if the small-dust surface density varies by a factor
of $\gtrsim30$ across the H$_2$O snow line. According to previous grain growth
simulations, this condition could be achieved by weak disk turbulence if
silicate grains are more fragile than icy grains. The shadow can cause the
condensation of most volatile substances, namely N$_2$ and Ar. We demonstrate
that the dissolution of shadowed solids can explain the elemental abundance
patterns of the Jovian atmosphere even if proto-Jupiter was formed near
Jupiter's current orbit. The disk shadow may play a vital role in controlling
atmospheric compositions. The effect of the shadow also impacts the
interpretation of upcoming observations of exoplanetary atmospheres by JWST.
