  A self-consistent two-dimensional model is proposed to account for the
transient mesospheric nighttime optical emissions associated to possible
intra-cloud (IC) lightning occurring in the Venusian troposphere. The model
calculates the mesospheric (between 75 km and 120 km in altitude)
quasielestrostatic electric field and electron density produced in response to
IC lightning activity located beween 40 km and 65 km in the Venusian cloud
layer. The optical signatures and the densities of perturbed excited atomic and
molecular neutral and ionic species in the mesosphere of Venus are also
calcutated using a basic kinetic scheme. The calculations were performed for
different IC lightning discharge properties [Krasnopolsky (1980), Cosmic.
Res.]. We found that the calculated electric fields in the mesosphere of Venus
are above breakdown values and that, consequently, visible transient glows
(similar to terrestrial Halos produced by lightning) right above the parent IC
lightning are predicted. The transient optical emissions result from radiative
de-excitation of excited electronic states of N$_2$ (in the ultraviolet,
visible and near infrared ranges) and of O($^{1}$S) and of O($^{1}$D) in,
respectively, the green (557 nm) and red (630 nm) wavelengths. The predicted
transient lightning induced glows from O($^{1}$S) can reach an intensity higher
than 167 R and, consequently, be above the detection threshold of the Lightning
and Airglow Camera (LAC) instrument aboard the japanese Akatsuki probe orbiting
Venus since Dec 2015. However, according to our model, successful observations
of transient lightning-induced optical glows could only be possible for
sufficiently close (300 km or maximum 1000 km) distances.
