A thermodynamically general theory for convective vortices

Convective vortices are common features of atmospheres that absorb lower-entropy-energy at higher temperatures than they reject higher-entropy-energy to space. These vortices range from small to large-scale and play an important role in the vertical transport of heat, momentum, and tracer species. Thus, the development of theoretical models for convective vortices is important to our understanding of some of the basic features of planetary atmospheres. The heat engine framework is a useful tool for studying convective vortices. However, current theories assume that convective vortices are reversible heat engines. Since there are questions about how reversible real atmospheric heat engines are, their usefulness for studying real atmospheric vortices is somewhat controversial. In order to reduce this problem, a theory for convective vortices that includes irreversible processes is proposed. The paper's main result is that the proposed theory provides an expression for the pressure drop along streamlines that includes the effects of irreversible processes. It is shown that a simplified version of this expression is a generalization of Bernoulli's equation to convective circulations. It is speculated that the proposed theory not only explains the intensity, but also sheds light on other basic features of convective vortices such as their physical appearance.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/73164/1/j.1600-0870.2008.00331.x.pd

Comments on the Search for Electrostatic Discharges on Mars

Ruf et al. used the Deep Space Network (DSN) to search for the emission of non-thermal radiation by martian dust storms, theoretically predicted by Renno et al. They detected the emission of non-thermal radiation that they were searching for, but were surprised that it contained spectral peaks suggesting modulation at various frequencies and their harmonics. Ruf et al. hypothesized that the emission of non-thermal radiation was caused by electric discharges in a deep convective dust storm, modulated by Schumann resonances (SRs). Anderson et al. used the Allen Telescope Array (ATA) to search for similar emissions. They stated that they found only radio frequency interference (RFI) during their search for non-thermal emission by martian dust storms and implicitly suggested that the signal detected by Ruf et al. was also RFI. However, their search was not conducted during the dust storm season when deep convective storms are most likely to occur. Here, we show that the ubiquitous dust devils and small-scale dust storms that were instead likely present during their observations are too shallow to excite SRs and produce the signals detected by Ruf et al. We also show that the spectral and temporal behavior of the signals detected by Anderson et al. corroborates the idea that they originated from man-made pulse-modulated telecommunication signals rather than martian electric discharges. In contrast, an identical presentation of the signals detected by Ruf et al. demonstrates that they do not resemble man-made signals. The presentation indicates that the DSN signals were consistent with modulation by martian SRs, as originally hypothesized by Ruf et al. We propose that a more comprehensive search for electrostatic discharges be conducted with either the ATA or DSN during a future martian dust storm season to test the hypothesis proposed by Ruf et al.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/98588/1/0004-637X_761_2_88.pd

Characterization of the Impingement Dynamics of Pulsed Rocket Plumes with the Ground at Low Ambient Pressure

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/76629/1/AIAA-2007-5707-681.pd

The role of convective plumes and vortices on the global aerosol budget

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95106/1/grl20113.pd

Probing Dust and Water in Martian Atmosphere with Far-Infrared Frequency Spacecraft Occultation

Airborne dust plays an active role in determining the thermal structure and chemical composition of the present-day atmosphere of Mars and possibly the planet's climate evolution over time through radiative--convective and cloud microphysics processes. Thus, accurate measurements of the distribution and variability of dust are required. Observations from the Mars Global Surveyor/Thermal Emission Spectrometer Mars Mars Reconnaissance Orbiter/Mars Climate Sounder and Mars Express/Fourier Transform Spectrometer and the Curiosity Rover have limited capability to measure dust. We show that spacecraft occultation of the Martian atmosphere at far-infrared frequencies between 1 and 10 THz can provide the needed global and temporal data on atmospheric dust by providing co-located measurements of temperature and dust opacity from the top of the atmosphere all the way down to the surface. In addition, spacecraft occultation by a small-satellite constellation could provide global measurements of the development of dust storms

Determination of dust aerosol particle size at Gale Crater using REMS UVS and Mastcam measurements

We calculate the seasonal and interannual variation in dust aerosol particle size above Gale Crater during the first 1413 Martian solar days (sols = 24.6 h) of the Mars Science Laboratory mission. Measurements of UV radiation made by the Rover Environmental Monitoring Station in combination with atmospheric opacities retrieved from the Mastcam instrument are used for the calculations. Our results indicate that the dust effective radius varies significantly with season, ranging from ~0.6 μm during the low opacity season (Ls = 60°â 140°) to ~2 μm during the high opacity season (Ls = 180°â 360°). Our results suggest that Gale Crater is affected by dust events of high aerosol content originated at various distances from it. Our results improve the accuracy of estimations of ultraviolet radiation fluxes at the Martian surface. Moreover, our results have important implications because the lifetime of suspended dust and its ability to nucleate clouds are affected by particle size.Plain Language SummaryThe Martian atmosphere transports large amounts of dust, which interacts strongly with solar and infrared radiation. The large spatial and temporal variability in atmospheric dust load creates complex feedbacks connecting dust lifting with the evolving atmospheric circulations. The size of suspended aerosols affects the surface and atmospheric heating rates, influencing the Martian climate. In this work, we have calculated the dust aerosol particle size above Gale Crater during the first 1413 sols of the Mars Science Laboratory (MSL) mission using measurements of UV radiation made for the first time from the surface of Mars. Our results indicate that the dust effective radius varies significantly with season, ranging from ~0.6 μm during the clear season to ~2 μm during the dusty season. Our results suggest that Gale Crater is affected by dust events of high aerosol content originated at various distances from it. Our results are important because the lifetime of suspended dust and its ability to nucleate clouds are affected by the particle size.Key PointsWe have developed a novel methodology to retrieve dust aerosol particle size at Gale Crater using Mars Science Laboratory dataThe retrieved dust effective radii range from 0.6 μm during the clear aphelion season to 2 μm during the dusty perihelion seasonOur results improve the estimation of ultraviolet radiation fluxes at the Martian surfacePeer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/137189/1/grl55782-sup-0001-2017GL072589-SI.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/137189/2/grl55782_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/137189/3/grl55782.pd

Electrostatics in wind-blown sand

Wind-blown sand, or "saltation," is an important geological process, and the primary source of atmospheric dust aerosols. Significant discrepancies exist between classical saltation theory and measurements. We show here that these discrepancies can be resolved by the inclusion of sand electrification in a physically based saltation model. Indeed, we find that electric forces enhance the concentration of saltating particles and cause them to travel closer to the surface, in agreement with measurements. Our results thus indicate that sand electrification plays an important role in saltation.Comment: 4 journal pages, 5 figures, and supplementary material. Article is in press at PR

MATADOR 2002: A pilot field experiment on convective plumes and dust devils

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/94607/1/jgre1827.pd

Underexpanded Supersonic Plume Surface Interactions: Applications for Spacecraft Landings on Planetary Bodies

Numerical and experimental investigations of both far-field and near-field supersonic steady jet interactions with a flat surface at various atmospheric pressures are presented in this paper. These studies were done in assessing the landing hazards of both the NASA Mars Science Laboratory and Phoenix Mars spacecrafts. Temporal and spatial ground pressure measurements in conjunction with numerical solutions at altitudes of approx.35 nozzle exit diameters and jet expansion ratios (e) between 0.02 and 100 are used. Data from steady nitrogen jets are compared to both pulsed jets and rocket exhaust plumes at Mach approx.5. Due to engine cycling, overpressures and the plate shock dynamics are different between pulsed and steady supersonic impinging jets. In contrast to highly over-expanded (e 5 (lunar atmospheric regime), the ground pressure is minimal due to the development of a highly expansive shock structure. We show this is dependent on the stability of the plate shock, the length of the supersonic core and plume decay due to shear layer instability which are all a function of the jet expansion ratio. Asymmetry and large gradients in the spatial ground pressure profile and large transient overpressures are predominantly linked to the dynamics of the plate shock. More importantly, this study shows that thruster plumes exhausting into martian environments possess the largest surface pressure loads and can occur at high spacecraft altitudes in contrast to the jet interactions at terrestrial and lunar atmospheres. Theoretical and analytical results also show that subscale supersonic cold gas jets adequately simulate the flow field and loads due to rocket plume impingement provided important scaling parameters are in agreement. These studies indicate the critical importance of testing and modeling plume-surface interactions for descent and ascent of spacecraft and launch vehicles