  The transverse momentum dependent helicity distributions of valence quarks
are calculated in the light-cone diquark model by adopting two different
approaches. We use the model results to analyze the $P_{h\perp}$-dependent
double spin asymmetries for $\pi^+$, $\pi^-$ and $\pi^0$ productions in
semi-inclusive deep inelastic scattering, and find that the asymmetries agree
with the CLAS data in one of the approaches. By taking the Fourier transform of
the transverse momentum dependent helicity distributions, we obtain the
helicity distributions of valence quarks in the transverse coordinate space,
and then apply them further to predict the Bessel-weighted double spin
asymmetries of $\pi^+$, $\pi^-$ and $\pi^0$ productions in semi-inclusive deep
inelastic scattering at CLAS, COMPASS and HERMES for the first time. The shape
of the Bessel-weighted double spin asymmetry thereby provides a direct probe on
the transverse structure of longitudinally polarized quarks.
