P081-0004
Planetary Scale Seasonal and Tidal Atmospheric Mass Transport: Role of Gradiometry Measurements

Wednesday, 16 December 2020
Poster
Bruce G Bills1, Michael Mischna2, Ryan S Park3, Mark J Lysek4, Ho Jung Paik5, M Vol Moody6, Christopher J Collins7 and Ronald S Norton7, (1)NASA Jet Propulsion Laboratory, Pasadena, CA, United States, (2)Jet Propulsion Laboratory, Pasadena, CA, United States, (3)JPL/NASA/Caltech, Pasadena, United States, (4)Jet Propulsion Laboratory, Pasadena, United States, (5)University of Maryland, San Jose, CA, United States, (6)University of Maryland College Park, Physics, College Park, MD, United States, (7)University of Maryland, College Park, United States
Abstract:
An improved understanding of atmospheric dynamics and near-surface processes on planets like Venus, Earth, and Mars can be obtained by sufficiently accurate measurements of the time variable gravity, associated with seasonal and tidal mass transport. For Earth, the GRACE and GRACE-Follow-On missions have already changed time variable gravity from a geodetic sub-discipline to a key feature of climate change studies. Current generation gravity models at Mars and Venus are not yet sufficiently accurate to make that conversion. However, near-term development of superconducting gravity gradiometer (SGG) instruments and associated missions, will soon change that situation.

Current instrument development is leading toward fabrication and testing of a full-tensor instrument with 1.4 ×10-4 Eotvos/Sqrt[Hz] sensitivity in the frequency band of 1 to 50 mHz and < 2 ×10-5 Eotvos/Sqrt[Hz] between 0.1 and 1 mHz . The SGG requires cooling to < 6 K, and the goal is to use a cryocooler to enable a mission lifetime of 5-10 years. There are candidate cryocoolers for a future SGG mission with negligible vibration.

Recent analyses provide a simple template for converting instrument performance, orbit geometry, and mission duration into estimates of the error spectrum. For thermal tides on Venus, GCM simulations have provided initial estimates of the signal spectrum. For seasonal transport on Mars, Viking Lander surface pressure measurements have been used to estimate the signal spectrum. Still somewhat unresolved, in both cases, is the SNR required to provide observational constraints on key system parameters.

In the case of thermal tides on Venus, the main unknown parameters controlling the spatial pattern of mass transport is the depth distribution of radiative absorption. Sufficiently accurate measurement of the tidal transport will provide new constraints on the absorption profile.

In the case of seasonal transport on Mars, a previous model has shown that adjusting 5 parameters (emissivity and albedo of each pole cap, and total mass of CO2 being transported) allows a good fit to the Viking Lander pressure observations. The Viking measurements have good temporal resolution, but only sample two surface locations. Having a global model of time variable gravity will be equivalent to having several hundred Viking Lander time series.

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