D. Grassi

First Estimate of Wind Fields in the Jupiter Polar Regions From JIRAM‐Juno Images

We present wind speeds at the ~ 1 bar level at both Jovian polar regions inferred from the 5-μm infrared images acquired by the Jupiter InfraRed Auroral Mapper (JIRAM) instrument on the National Aeronautics and Space Administration Juno spacecraft during its fourth periapsis (2 February 2017). We adopted the criterion of minimum mean absolute distortion (Gonzalez & Woods, 2008) to quantify the motion of cloud features between pairs of images. The associated random error on speed estimates is 12 m/s in the northern polar region and 9.8 m/s at the south. Assuming that polar cyclones described by Adriani et al. (2018, https://doi.org/10.1038/nature25491) are in rigid motion with respect to System III, tangential speeds in the interior of the vortices increase linearly with distance from the center. The annulus of maximum speed for the main circumpolar cyclones is located at approximatively 1,000 km from their centers, with peak cyclonic speeds typically between 80 and 110 m/s and ~50 m/s in at least two cases. Beyond the annulus of maximum speed, tangential speed decreases inversely with the distance from the center within the Southern Polar Cyclone and somewhat faster within the Northern Polar Cyclone. A few small areas of anticyclonic motions are also identified within both polar regions.

ACS/TIRVIM: Calibration and first results

Atmospheric Chemistry Suite (ACS) is a part of Russian contribution to ExoMars Trace Gas Orbiter (TGO) ESA-Roscosmos mission. ACS includes three separate infrared spectrometers (MIR, NIR and TIRVIM) with a different spectral coverage and targeted to the different science goals. ACS TIRVIM is a Fourier-transform spectrometer based on 2-inch double pendulum interferometer. It operates in the spectral range of 1.7-7 μm with the best spectral resolution 0.13 cm-1 for solar occultation (SO) mode and 0.8 cm-1 for nadir mode. In nadir mode TIRVIM is purposed to thermal sounding of the Martian atmosphere and aerosol properties retrieval. In SO mode TIRVIM is dedicated to trace gases measurements complementing to ACS MIR. After successful launch of ExoMars TGO on 16 April 2016 there were three time slots for turning on science instruments during cruise phase to execute necessary checks and calibration measurements. In March 2018 the nominal science orbit was reached after cruise and aerobraking phases. The first results of TIRVIM data processing show high performance of the instrument.