# # Program information file # PROGRAM_ID 2023B086 PROGRAM_TITLE Venus Dayside at 4 microns PROGRAM_INV1 Kandis Lea Jessup PROGRAM_INV2 Takao Sato PROGRAM_INV3 Hideo Sagawa PROGRAM_INV4 Eliot Young PROGRAM_INV5 Franklin Mills PROGRAM_SCICAT major planets / satellites PROGRAM_ABSTRACT_BEG We propose to use iSHELL's high spectral resolution capabilities to unambiguously define the Venus cloud top altitude while monitoring the abundance of trace gases detectable on the Venus dayside near 4 um such as SO2 and HCl. These observations will support the interpretation of Venus cloud top observations made at UV wavelengths by active missions such as Bepi Colombo and Akatsuki, during coordinated Venus observation campaigns planned for the Fall of 2023. These observations will advance studies of Venus atmospheric structure, and support long-term observing programs focused on tracing impact of Venus's most prominent cloud top absorbing species on climate trends, solar heating and convective activity at the Venus cloud top through time. Our requested time intersects with coordinated Bepi-Akatsuki UV observing planned for October 22-24. To understand climatic patterns, it is important to define the stability and time scale of variability of the cloud top properties on seasonal i.e. ~ 30 day, timescales. Therefore, we are requesting 2 observing runs, providing a total of 20 days observing, using 4 hours per date of observation within a 30-day period. Venus will be visible in the daytime, between ~ 17 and 22 UT [~ 7 a.m. and noon Hawaii time] We are requesting repeated periods of consecutive days of observation, to adequately identify the timescale on which trace species at the Venus cloud top and/or the altitude of cloud top may vary, relative to any changes in the vertical exchange occurring within Hadley-cell like convection processes, that are anticipated to require 3 to 5 days to be perceptible at the Venus cloud top. On each date of observation, multiple latitudes on the Venus disk will be observed, allowing us to assess how the trace gas abundance and cloud top altitude varies with latitude and on average on the Venus dayside. PROGRAM_ABSTRACT_END