  Our study aims to investigate the outer disc structure of the Milky Way
galaxy using the red clump (RC) stars. We analysed the distribution of the
largest sample of RC stars to date, homogeneously covering the entire Galactic
plane in the range of $40^\circ \le \ell \le 340^\circ$ and $-10^\circ \le b
\le +10^\circ$. This sample allows us to model the RC star distribution in the
Galactic disc to better constrain the properties of the flare and warp of the
Galaxy. Our results show that the scale length of the old stellar disc weakly
depends on azimuth, with an average value of $1.95 \pm0.26$ kpc. On the other
hand, a significant disc flaring is detected, where the scale height of the
disc increases from 0.38 kpc in the solar neighbourhood to $\sim 2.2$ kpc at R
$\approx 15$ kpc. The flare exhibits a slight asymmetry, with $\sim 1$ kpc more
scale height below the Galactic plane as compared to the Northern flare. We
also confirm the warping of the outer disc, which can be modelled with $Z_w =
(0.0057 \pm 0.0050)~ [R-(7358 \pm 368) (pc)]^{1.40 \pm 0.09} \sin(\phi -
(-2^\circ.03 \pm 0^\circ .18))$. Our analysis reveals a noticeable north-south
asymmetry in the warp, with a greater amplitude observed in the southern
direction compared to the northern. Comparing our findings with younger tracers
from the literature, we observe an age dependency of both the flare and warp.
An increase in flare strength with age suggests the secular evolution of the
disc as the preferred mechanism for forming the flare. The increase of the
maximum warp amplitude with age indicates that the warp dynamics could be the
possible cause of the variation in the warp properties with age.

Astrophysics of Galaxies