  Observed chemical species in the Venusian mesosphere show local-time
variabilities. SO2 at the cloud top exhibits two local maxima over local time,
H2O at the cloud top is uniformly distributed, and CO in the upper atmosphere
shows a statistical difference between the two terminators. In this study, we
investigated these local-time variabilities using a three-dimensional (3D)
general circulation model (GCM) in combination with a two-dimensional (2D)
chemical transport model (CTM). Our simulation results agree with the observed
local-time patterns of SO2, H2O, and CO. The two-maximum pattern of SO2 at the
cloud top is caused by the superposition of the semidiurnal thermal tide and
the retrograde superrotating zonal (RSZ) flow. SO2 above 85 km shows a large
day-night difference resulting from both photochemistry and the sub-solar to
anti-solar (SS-AS) circulation. The transition from the RSZ flows to SS-AS
circulation can explain the CO difference between two terminators and the
displacement of the CO local-time maximum with respect to the anti-solar point.
H2O is long-lived and exhibits very uniform distribution over space. We also
present the local-time variations of HCl, ClO, OCS and SO simulated by our
model and compare to the sparse observations of these species. This study
highlights the importance of multidimensional CTMs for understanding the
interaction between chemistry and dynamics in the Venusian mesosphere.
