  In event by event hydrodynamic model, we have simulated 30-40\% Au+Au
collisions at RHIC and computed the slope parameter from the invariant pion
distribution. In each event, the slope parameter fluctuates azimuthally.
Fourier expansion coefficients $T_n$ for the slope parameter and the Fourier
expansion coefficients $v_n$ for the azimuthal distribution $\frac{dN}{d\phi}$
are found to be strongly correlated. Strong correlation between the two
expansion coefficients suggests that in addition to azimuthal distribution,
fluctuations in the slope parameter of the invariant distribution can as well
be used to study the final state momentum anisotropy in relativistic energy
heavy ion collisions. If measured experimentally, they can serve as additional
constraint for hydrodynamical modeling.
