For cables in troughs, this is the temperature of the ambient air above ground. This is taken as the inital air temperature inside the air-filled trough.

Symbol
$\theta_{\mathrm{air}}$
Unit
°C
Used in
$\alpha_{\mathrm{gas}}$
$c_{\mathrm{p_{\mathrm{gas}}}}$
$\Delta \theta_{\mathrm{c}}$
$\eta_{\mathrm{gas}}$
$I_{\mathrm{c}}$
$k_{\mathrm{gas}}$
$\mathrm{Pr}_{\mathrm{gas}}$
$\rho_{\mathrm{gas}}$
Gas density [kg/m³]
$\theta_{\mathrm{at}}$
$\theta_{\mathrm{c}}$