Geological and geophysical field investigations from a lunar base at Mare Smythii

Mare Smythii, located on the equator and east limb of the Moon, has a great variety of scientific and economic uses as the site for a permanent lunar base. Here a complex could be established that would combine the advantages of a nearside base (for ease of communications with Earth and normal operations) with those of a farside base (for shielding a radio astronomical observatory from the electromagnetic noise of Earth). The Mare Smythii region displays virtually the entire known range of geological processes and materials found on the Moon; from this site, a series of field traverses and investigations could be conducted that would provide data on and answers to fundamental questions in lunar geoscience. This endowment of geological materials also makes the Smythii region attractive for the mining of resources for use both on the Moon and in Earth-Moon space. We suggest that the main base complex be located at 0, 90 deg E, within the mare basalts of the Smythii basin; two additional outposts would be required, one at 0, 81 deg E to maintain constant communications with Earth, and and the other, at 0, 101 deg E on the lunar farside, to serve as a radio astronomical observatory. The bulk of lunar surface activities could be conducted by robotic teleoperations under the direct control of the human inhabitants of the base

The frequency of compound chondrules and implications for chondrule formation

Abstract-The properties of compound chondrules and the implications that they have for the conditions and environment in which chondrules formed are investigated. Formulae to calculate the probability of detecting compound chondrules in thin sections are derived and applied to previous studies. This reinterpretation suggests that at least 5% of chondrules are compounds, a value that agrees well with studies in which whole chondrules were removed from meteorites. The observation that adhering compounds tend to have small contact arcs is strengthened by application of these formulae. While it has been observed that the secondaries of compound chondrules are usually smaller than their primaries, these same formulae suggest that this could be an observation bias. It is more likely than not that thin section analyses will identify compounds with secondaries that are smaller than their primaries. A new model for chondrule collisional evolution is also developed. From this model, it is inferred that chondrules would have formed, on average, in areas of the solar nebula that had solids concentrated at least 45 times over the canonical solar value

Short-Term Solar Modulation of the Madden-Julian Climate Oscillation

Normalized occurrence rates of daily Madden-Julian oscillation (MJO) events are calculated as a function of phase lag relative to peaks and minima in solar ultraviolet flux occurring on the solar rotational time scale (similar to 27 days). All MJO phases and four solar maximum periods are considered (1979-83, 1989-93, 1999-2003, and 2011-15). Corresponding daily static stabilities in the tropical lower stratosphere (70-100 hPa) are calculated from ERA-Interim data and are averaged over the warm pool region. The statistical significance of occurrence-rate changes following UV peaks and minima is assessed using a Monte Carlo method. When MJO events with amplitudes greater than about 2 are considered during the December-May period (about 15% of those days), significant reductions of MJO occurrence rates and associated increases in static stability in the tropical lower stratosphere are obtained 1-7 days following solar UV peaks. Consistently, cross-correlation analyses of high-pass-filtered daily MJO amplitudes and solar UV flux during the same seasonal period produce significant negative correlations near and following solar UV peaks. Conversely, mean occurrence rates are increased and lower-stratospheric static stabilities are decreased following solar UV minima. The reductions (increases) in occurrence rate following solar UV peaks (minima) are largest when the stratospheric quasi-biennial oscillation is in its easterly phase. Little or no dependence of the solar modulation on the phase of El Nino-Southern Oscillation is obtained.Climate and Large-Scale Dynamics branch of the National Science Foundation [1643160]6 month embargo; published online: 6 March 2018This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

The Lower-Stratospheric Response to 11-Yr Solar Forcing: Coupling to the Troposphere–Ocean Response

The origin of the tropical lower-stratospheric response to 11-yr solar forcing and its possible coupling to a troposphere–ocean response is investigated using multiple linear regression (MLR) analyses of stratospheric ozone and temperature data over the 1979–2009 period and tropospheric sea level pressure (SLP) data over the 1880–2009 period. Stratospheric MLR results, comparisons with simulations from a chemistry–climate model, and analyses of decadal variations of meridional eddy heat flux indicate that the tropical lower-stratospheric response is produced mainly by a solar-induced modulation of the Brewer–Dobson circulation (BDC), with a secondary contribution from the Hadley circulation in the lowermost stratosphere. MLR analyses of long-term SLP data confirm previous results indicating a distinct positive response, on average, during the northern winter season in the North Pacific. The mean response in the Northern Hemisphere resembles a positive Arctic Oscillation mode and can also be characterized as “La Niña–like,” implying a reduction of Rossby wave forcing, a weakening of the BDC, and an increase in tropical lower-stratospheric ozone and temperature near solar maxima. However, MLR analyses of different time periods show that the Pacific SLP response is not always present during every cycle; it was most clearly detected mainly during the ~1938–93 period when 11-yr solar variability was especially strong. During the 1979–93 period, the SLP response was strongly present when the lower-stratospheric responses were large. But during the 1994–2009 period, the SLP response was much less significant and the lower-stratospheric responses were weak, supporting the hypothesis that the lower-stratospheric and surface climate responses are dynamically coupled.The stratospheric MLR analyses were supported in part under Grant NNX10AQ63G from the NASA Living With a Star Targeted Research and Technology program and in part through a subcontract from the Naval Research Laboratory under Grant NNH08AI67 (J. McCormack, P.I.) issued through the LWS TR&T program. Comparisons with WACCM model simulations are supported under a grant from the Climate Dynamics branch of the National Science Foundation.6 month embargo: Published Online: 5 June 2012This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

Constraining the Early History of Mercury and Its Core Dynamo by Studying the Crustal Magnetic Field

International audienceKey Points: 9 • We analyze crustal magnetic anomalies that are likely thermoremanent and ob-10 tain the corresponding paleopole positions. 11 • All best fitting paleopoles are found in the Southern Hemisphere. 12 • Our study strongly suggests that Mercury has evolved with time. Abstract 14 Low altitude magnetic field data acquired by MESSENGER over a small portion of Mer-15 cury's surface revealed weak crustal magnetic field signatures. Here we study the crustal 16 magnetic anomalies associated with impact craters on Mercury. We assume that the sources 17 of these anomalies consist of impact melt, enriched in impactor iron. We assume that 18 the subsurfaces of Mercury's impact craters have cooled in the presence of a constant 19 global magnetic field, thus becoming thermoremanently magnetized. We invert for the 20 crustal magnetization direction within five craters using a unidirectional magnetization 21 model which assumes that the melt impact rocks recorded the constant core magnetic 22 field present when the crater was formed, and that the crater's magnetization has not 23 been altered since its formation. From the best fitting magnetization direction we then 24 obtain the corresponding north magnetic paleopole position assuming a centered core 25 dipolar field. Results show that all five magnetic paleopoles lie in the Southern Hemi-26 sphere but are not required to be located near the present-day magnetic pole, which lies 27 near the south geographic pole. Accounting for the uncertainties, we show that our re-28 sults all agree in a common small region that excludes the current magnetic pole. This 29 strongly suggests that the dynamo has evolved with time. Our results represent valu-30 able information for understanding the evolution of Mercury, and emphasize the impor-31 tance of including more anomaly analyses to complete and refine our conclusions. 3

Possible solar modulation of the equatorial quasi-biennial oscillation: Additional statistical evidence

Although the quasi-biennial oscillation (QBO) in the equatorial zonal wind is dominantly driven by wave forcing originating in the troposphere, a recent study suggests that certain properties of the QBO may vary slightly on the 11-year solar cycle timescale [Salby and Callaghan, 2000]. Here we report further statistical investigation using both equatorial wind data for levels from 50 to 1 hPa and longterm proxy solar ultraviolet flux time series (10.7-cm solar radio flux and sunspot numbers). Spectral analysis of the solar time series yields evidence for a significant spectral peak at periods between 25 and 30 months, approximately equivalent to the mean QBO period, as had also been noted by earlier authors [Shapiro and Ward, 1962]. Cross-spectral analysis of the 10.7-cm solar radio flux and equatorial zonal wind time series shows significant coherency at the QBO period at all available pressure levels. The phase lag of the wind data relative to the solar flux at the QBO period ranges from 0–1 months near the stratopause (1 hPa) to 20–24 months in the lower stratosphere (50 hPa). The nearly inphase relationship near the stratopause suggests a possible modulation of the QBO at this level by the radiative and photochemical effects of solar ultraviolet variations. The amplitudes of the solar variations at the QBO period tend to be larger under solar maximum than under solar minimum conditions. Composite analysis of the westerly and easterly phases of the equatorial zonal wind shows subtle but consistent differences in the durations of the westerlies and easterlies between solar maximum and minimum conditions.6 month embargo; First published: 1 July 2001This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

Magnetic anomalies in the Imbrium and Schrödinger impact basins: Orbital evidence for persistence of the lunar core dynamo into the Imbrian epoch

Approximate maps of the lunar crustal magnetic field at low altitudes in the vicinities of the three Imbrian-aged impact basins, Orientale, Schrdinger, and Imbrium, have been constructed using Lunar Prospector and Kaguya orbital magnetometer data. Detectable anomalies are confirmed to be present well within the rims of Imbrium and Schrdinger. Anomalies in Schrdinger are asymmetrically distributed about the basin center, while a single isolated anomaly is most clearly detected within Imbrium northwest of Timocharis crater. The subsurface within these basins was heated to high temperatures at the time of impact and required long time periods (up to 1 Myr) to cool below the Curie temperature for metallic iron remanence carriers (1043 K). Therefore, consistent with laboratory analyses of returned samples, a steady, long-lived magnetizing field, i.e., a former core dynamo, is inferred to have existed when these basins formed. The asymmetrical distribution within Schrdinger suggests partial demagnetization by later volcanic activity when the dynamo field was much weaker or nonexistent. However, it remains true that anomalies within Imbrian-aged basins are much weaker than those within most Nectarian-aged basins. The virtual absence of anomalies within Orientale where impact melt rocks (the Maunder Formation) are exposed at the surface is difficult to explain unless the dynamo field was much weaker during the Imbrian period.6 month embargo; First published: 15 November 2016This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

The Planetesimal Bow Shock Model for Chondrule Formation: More Detailed Simulations in the Near Vicinity of the Planetesimal

Gas dynamic shock waves in a low temperature nebula have been considered to be a leading candidate mechanism for providing the repetitive, short-duration heating events that are believed to have been responsible for the formation of chondrules in chondrites. It has been found, for example, that shocks with Mach numbers greater than 4 or 5 would be capable of rapidly melting 0.1-1 mm sized silicate particles as required by meteoritic data. Near the nebula midplane where chondrite parent bodies are believed to have formed, possible energy sources for generating multiple shocks include mass concentrations in a gravitationally unstable nebula, tidal interactions of proto-Jupiter with the nebula, and bow waves upstream of planetesimals scattered gravitationally into eccentric orbits by proto- Jupiter. In a recent study, we have found that chondrule precursors that are melted following passage through a planetesimal bow shock would likely cool at rates that are too rapid to be consistent with meteoritic evidence. However, that study was limited to the bowshock exterior to about 1.5 planetesimal radii (measured perpendicular to the symmetry axis) to avoid complications interior to this distance where large pressure gradients and lateral flow occur as the gas flows around the planetesimal. In this paper, we reconsider the planetesimal bow shock model and report more detailed numerical simulations of chondrule precursor heating, cooling, and dynamical histories in the near vicinity of a representative planetesimal

A partial correlation analysis of the stratospheric ozone response to 27-day solar UV variations with temperature effect removed

Observational detection of upper stratospheric ozone responses to 27-day solar ultraviolet (UV) variations is often inhibited by larger, dynamically induced ozone variations, which result mainly from the temperature dependence of reaction rates controlling the ozone balance. Here we show that partial correlation coefficients of solar UV and tropical upper stratospheric ozone (1–5 hPa) with the temperature effect removed are larger (07–0.8) than are total correlation coefficients of ozone and solar UV (0.4–0.6). The phase lag of ozone relative to solar UV is also increased, and the maximum ozone-UV correlation is obtained at higher altitudes, as compared with correlation analyses using ozone and solar UV data alone. Assuming that temperature variations are not forced by solar UV variations, the ozone sensitivity to solar UV and temperature can be calculated using a linear multiple regression model. The ozone sensitivity to solar UV is generally independent of time periods used for the analysis. However, the magnitude of the ozone sensitivity to temperature at 1–2 hPa increased significantly from solar cycle 21 to solar cycle 22, possibly reflecting long-term changes in the composition of the upper stratosphere.This work is partly supported by the NASA Upper Atmosphere Research Satellite (UARS) program.6 month embargo; First published: 1 February 2000This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

Evaluating planetesimal bow shocks as sites for chondrule formation

We investigate the possible formation of chondrules by planetesimal bow shocks. The formation of such shocks is modeled using a piecewise parabolic method (PPM) code under a variety of conditions. The results of this modeling are used as a guide to study chondrule formation in a one-dimensional, finite shock wave. This model considers a mixture of chondrule-sized particles and micron-sized dust and models the kinetic vaporization of the solids. We found that only planetesimals with a radius of ~1000 km and moving at least ~8 km/s with respect to the nebular gas can generate shocks that would allow chondrule-sized particles to have peak temperatures and cooling rates that are generally consistent with what has been inferred for chondrules. Planetesimals with smaller radii tend to produce lower peak temperatures and cooling rates that are too high. However, the peak temperatures of chondrules are only matched for low values of chondrule wavelength-averaged emissivity. Very slow cooling (<~100s of K/hr) can only be achieved if the nebular opacity is low, which may result after a significant amount of material has been accreted into objects that are chondrule-sized or larger, or if chondrules formed in regions of the nebula with small dust concentrations. Large shock waves of approximately the same scale as those formed by gravitational instabilities or tidal interactions between the nebula and a young Jupiter do not require this to match the inferred thermal histories of chondrules.The Meteoritics & Planetary Science archives are made available by the Meteoritical Society and the University of Arizona Libraries. Contact [email protected] for further information.Migrated from OJS platform February 202