Engineering topics

Wilson, R. John

Publications and source records attributed to Wilson, R. John.

4 records

NASA NTRS2018

High-Resolution Modeling of the Dust and Water Cycles with the NASA Ames Mars Global Climate Model

NASA’s Mars Climate Modeling Center at Ames Research Center is currently undergoing an exciting period of growth in personnel, modeling capabilities, and science productivity. We are transitioning from our legacy Arakawa C-grid finite-difference dynamical core to the NOAA/GFDL cubed-sphere finite-volume dynamical core for simulating the climate of Mars in a global framework. This highly parallelized core is scalable and flexible, which allows for significant improvements in the horizontal and vertical resolutions of our simulations. We have implemented the Ames water ice cloud microphysics package described in Haberle et al. (2018) into this new dynamical core. We will present high-resolution simulations of the dust and water cycles that show that sub-degree horizontal resolution improves the agreement between the vertical distribution of dust and water ice and observations. In particular, both water ice clouds and dust are transported to higher altitudes due to stronger topographic circulations at high resolution. Preliminary results suggest that high-resolution global modeling is needed to properly capture critical features of the dust and water cycles, and thus the current Mars climate.

Kahre, Melinda A.↗

NASA NTRS2015

The Solsticial Pause on Mars: A Planetary Wave Reanalysis - Part 1

Large-scale planetary waves are diagnosed from an analysis of profiles retrieved from the Thermal Emission Spectrometer aboard the Mars Global Surveyor spacecraft during its scientific mapping phase. The analysis is conducted by assimilating thermal profiles and total dust opacity retrievals into a Mars global circulation model. Transient waves are largest throughout the northern hemisphere autumn, winter and spring period and almost absent during the summer. The southern hemisphere exhibits generally weaker transient wave behavior. A striking feature of the low-altitude transient waves in the analysis is that they show a broad subsidiary minimum in amplitude centred on the winter solstice, a period when the thermal contrast between the summer hemisphere and the winter pole is strongest and baroclinic wave activity might be expected to be strong. This behavior, here called the 'solsticial pause,' is present in every year of the analysis. This strong pause is under-represented in many independent model experiments, which tend to produce relatively uniform baroclinic wave activity throughout the winter. This paper documents and diagnoses the transient wave solsticial pause found in the analysis; a companion paper investigates the origin of the phenomenon in a series of model experiments.

Lewis, Stephen R.↗

NASA NTRS2014

Thermal Tides During the 2001 Martian Global-Scale Dust Storm

The 2001 (Mars Year 25) global dust storm radically altered the dynamics of the Martian atmosphere. Using observations from the Thermal Emission Spectrometer onboard the Mars Global Surveyor spacecraft and Mars WRF general circulation model simulations, we examine the changes to thermal tides and planetary waves caused by the storm. We find that the extratropical diurnal migrating tide is dramatically enhanced during the storm, particularly in the southern hemisphere, reaching amplitudes of more than 20 K. The tropical diurnal migrating tide is weakened to almost undetectable levels. The diurnal Kelvin waves are also significantly weakened, particularly during the period of global expansion at Ls=200deg-210deg. In contrast, the westward propagating diurnal wavenumber 2 tide strengthens to 4-8 K at altitudes above 30km. The wavenumber 1 stationary wave reaches amplitudes of 10-12 K at 50deg-70degN, far larger than is typically seen during this time of year. The phase of this stationary wave and the enhancement of the diurnal wavenumber 2 tide appear to be responses to the high-altitude westward propagating equatorial wavenumber 1 structure in dust mixing ratio observed during the storm in previous works. This work provides a global picture of dust storm wave dynamics that reveals the coupling between the tropics and high-latitude wave responses. We conclude that the zonal distribution of thermotidal forcing from atmospheric aerosol concentration is as important to understanding the atmospheric wave response as the total global mean aerosol optical depth.

Thermal tides↗

NASA NTRS1993

Three-dimensional numerical simulation of thermal tides in the Martian atmosphere

Analysis of the Mariner 9 IRIS and Viking Orbiter IRTM temperature data and of the time series of surface pressure from the Viking landers has indicated that atmospheric thermal tides are a significant component of the martian general circulation. Classical tidal theory, considering only the Sun synchronous components, has been shown to at least roughly account for the amplitudes of the observed diurnal and semidirunal surface pressure oscillations. In particular, Zurek and Leovy have demonstrated that classical tidal theory can reproduce the observed dependence of the strength of the semidiurnal tide on aerosol optical depth. The high-amplitude topograph of Mars, however, can cause longitudinal distortions in the thermotidal forcing, leading to additional tidal modes that are not Sun synchronous. In particular, observation and theory have suggested the likely presence of a diurnal, zonal wavenumber-1 K wave. Hamilton and Garcia noted that the wavenumber-1 K normal mode has a period of close to 24 hr and may be detectable in surface pressure observations. Zurek has discussed the possibility of this mode being resonantly excited for various atmospheric temperature studies. The semidiurnal wavenumber-2 K mode, with roughly a 12-hr period, could also be resonantly excited. A numerical model with finite amplitude topography and a self-consistent thermotidal forcing resulting from the daily heat flux at the surface and atmospheric absorption of solar radiation by aerosols is used here to explore the influence of topography on martian thermal tides and to examine the possibility of Kelvin wave resonance.

Wilson, R. John↗