Jeans escape parameter ($\lambda$)

For particles of mass $m$ at radius $r$ and temperature $T$, the Jeans escape parameter isLarge $\lambda$ gives weak tail escape, while order-unity $\lambda$ indicates hydrodynamic blow-off.

For exobase number density $n_e$ and $v_{\mathrm{th}}=\sqrt{2k_{B}T/m}$, the collisionless Jeans number flux is