# # Program information file # PROGRAM_ID 2023B082 PROGRAM_TITLE First day/night observations of OCS at the cloud-top of Venus: key diagnostic to vertical transport and chemistry in the Venus atmosphere PROGRAM_INV1 Hideo Sagawa PROGRAM_INV2 Shohei Aoki PROGRAM_INV3 Takao Sato PROGRAM_INV4 PROGRAM_INV5 PROGRAM_SCICAT major planets / satellites PROGRAM_ABSTRACT_BEG Despite recent advances in the Venusian atmospheric study, the atmospheric chemistry and the efficiency of vertical atmospheric diffusion at the cloud-top altitudes are still poorly understood. Carbonyl sulfide, OCS, abundance at the cloud-top can be a key diagnostic to these missing knowledge. However, only a few measurements of OCS are available in the literature. Moreover, the previous measurements are limited to the dayside of Venus. Measuring day to night variation of OCS abundances at the cloud top is indispensable to quantitatively constrain the eddy diffusion coefficient and diurnal photochemical processes of sulfur-carbon cycles. Thus, we propose a high-spectral resolution spectroscopy of M-band with IRTF/iSHELL, which is able to measure OCS abundances both on dayside and nightside of the Venus cloud-top for the first time. In order to precisely measure the OCS diurnal variation, we require the sensitivity that measures 10 ppb OCS absorption feature with S/N of 30. Our simulations with radiative transfer calculations and the iSHELL Exposure Time Calculator show that the required sensitivity will be achieved by the observations for 4.5 hours in total [including overheads]. The latitudinal distribution of OCS will be also investigated by observing at two different latitudes, equator and middle latitudes. In total, we request 4.5 hours observation for two successive days. IRTF is a unique facility to perform this proposed Venus observation since it is allowed to operate during daytime. 2023B semester covers the period when Venus is at its largest solar elongation, therefore it is particularly suitable for the proposed observation since we will be able to observe both day and night side of Venus together at the same time. PROGRAM_ABSTRACT_END