Search

A modulation has been identified of the tropical Madden‐Julian oscillation (MJO) by the stratospheric quasi‐biennial oscillation (QBO) such that the MJO in boreal winter is ∼40% stronger and persists ∼10 days longer during the easterly QBO phase (QBOE) than during the westerly phase. A proposed mechanism is reductions of tropical lower stratospheric static stability during QBOE caused by (a) the QBO induced meridional circulation; and (b) QBO influences on extratropical wave forcing of the stratospheric residual meridional circulation during early winter. Here, long‐term variability of the QBO‐MJO connection and associated variability of near‐tropopause tropical static stability and extratropical wave forcing are investigated using European Center reanalysis data for the 1959–2021 period. During the most reliable (post‐satellite) part of the record beginning in 1979, a strengthening of the QBO‐MJO modulation has occurred during a time when tropical static stability in the lowermost stratosphere and uppermost troposphere has been decreasing and extratropical wave forcing in early winter has been increasing. A high inverse correlation (R = −0.87) is obtained during this period between early winter wave forcing anomalies and wintertime tropical lower stratospheric static stability. Regression relationships are used to show that positive trends in early winter wave forcing during this period have likely contributed to decreases in tropical static stability, favoring a stronger QBO‐MJO connection. As shown in previous work, increased sea level pressure anomalies over northern Eurasia produced by Arctic sea ice loss may have been a significant source of the observed positive trends in early winter wave forcing. Plain Language Summary: The tropical Madden‐Julian oscillation, also called the 40–50‐day oscillation, is a propagating pattern of tropical convection and precipitation that is a major driver of intraseasonal climate variability. Recent studies have found that (a) it is modulated by stratospheric forcings like the quasi‐biennial oscillation (QBO); and (b) the QBO modulation appears to have been strengthening since the early 1980s. A possible cause of the QBO modulation is reductions of static stability (stability against convection) near the tropical tropopause, which tend to occur during the easterly phase of the QBO. Consistent with this possible cause, tropical lower stratospheric static stabilities have been declining since the most reliable observations began in the late 1970s. Here, it is shown that increased tropical upwelling rates resulting from long‐term positive trends in early winter extratropical wave forcing of the stratospheric circulation have contributed significantly to the observed decline in tropical lower stratospheric static stability in boreal winter since that time. Increased sea level pressure anomalies over northern Eurasia produced by Arctic sea ice loss (and associated increases in Eurasian snow cover) can potentially explain the observed positive trends in early winter wave forcing. Climate model experiments are needed to test this possibility. Key Points: A stronger modulation of the Madden‐Julian oscillation by the stratospheric quasi‐biennial oscillation has existed since the early 1980sTropical stratospheric static stability has declined since the late 1970s due partly to increases in early winter extratropical wave forcingLarger sea level pressure anomalies over northern Eurasia due to Arctic sea ice loss are a possible cause of the increasing wave forcing [ABSTRACT FROM AUTHOR]

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.icarus.2010.01.009 Byline: Lon L. Hood (a), Keith P. Harrison (b), Benoit Langlais (c)(d), Robert J. Lillis (e), Francois Poulet (f), David A. Williams (g) Keywords: Mars; Magnetic fields; Mars, Interior; Mars, Surface Abstract: The nature of strong martian crustal field sources is investigated by mapping and modeling of Mars Global Surveyor magnetometer data near Apollinaris Patera, a previously proposed volcanic source, supplemented by large-scale correlative studies. Regional mapping yields evidence for positive correlations of orbital anomalies with both Apollinaris Patera and Lucus Planum, a nearby probable extrusive pyroclastic flow deposit that is mapped as part of the Medusae Fossae Formation. Iterative forward modeling of the Apollinaris Patera magnetic anomaly assuming a source model consisting of one or more uniformly magnetized near-surface disks indicates that the source is centered approximately on the construct with a scale size several times larger and comparable to that of the Apollinaris Patera free-air gravity anomaly. A significantly lower rms deviation is obtained using a two-disk model that favors a concentration of magnetization near the construct itself. Estimates for the dipole moment per unit area of the Lucus Planum source together with maximum thicknesses of [approximately equal to]3km based on topographic and radar sounding data lead to an estimated minimum magnetization intensity of [approximately equal to]50A/m within the pyroclastic deposits. Intensities of this magnitude are similar to those obtained experimentally for Fe-rich Mars analog basalts that cooled in an oxidizing (high fO.sub.2) environment in the presence of a strong ([greater than or equal to]10[mu]T) surface field. Further evidence for the need for an oxidizing environment is provided by a broad spatial correlation of the locations of phyllosilicate exposures identified to date using Mars Express OMEGA data with areas containing strong crustal magnetic fields and valley networks in the Noachian-aged southern highlands. This indicates that the presence of liquid water, which is a major crustal oxidant, was an important factor in the formation of strong magnetic sources. The evidence discussed here for magnetic sources associated with relatively young volcanic units suggests that a martian dynamo existed during the late Noachian/early Hesperian, after the last major basin-forming impacts and the formation of the northern lowlands. Author Affiliation: (a) Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ 85721, USA (b) Southwest Research Institute, Boulder, CO 80309, USA (c) Universite de Nantes, Laboratoire de Planetologie et Geodynamique, Nantes F-44000, France (d) CNRS, UMR 6112, Nantes F-44000, France (e) Space Sciences Laboratory, University of California, Berkeley, CA 94720, USA (f) CNRS, Universite Paris-Sud, Orsay, France (g) School of Earth and Space Exploration, Arizona State University, Tempe, AZ 85281, USA Article History: Received 29 January 2009; Revised 10 January 2010; Accepted 12 January 2010

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.icarus.2007.08.023 Byline: Lon L. Hood (a), Natalia A. Artemieva (b)(c) Keywords: Moon; Magnetic fields; Moon; interior; Moon; surface Abstract: 3D simulations of basin-scale lunar impacts are carried out to investigate: (a) the origins of strong crustal magnetic fields and unusual terrain observed to occur in regions antipodal to young large basins; and (b) the origin of enhanced magnetic and geochemical anomalies along the northwest periphery of the South Pole-Aitken (SPA) basin. The simulations demonstrate that a basin-forming impact produces a massive, hot, partially ionized cloud of vapor and melt that expands thermally around the Moon, converging near the basin antipode approximately 1 h after the impact for typical impact parameters. In agreement with previous work, analytic calculations of the interaction of this vapor-melt cloud with an initial ambient magnetic field predict a substantial temporary increase in field intensity in the antipodal region. The time of maximum field amplification coincides with a period when impacting ejecta also converge near the antipode. The latter produce antipodal shock stresses within the range of 5-25 GPa where stable shock remanent magnetization (SRM) of lunar soils has been found experimentally to occur. Calculated antipodal ejecta thicknesses are only marginally sufficient to explain the amplitudes of observed magnetic anomalies if mean magnetization intensities are comparable to those produced experimentally. This suggests that pre-existing ejecta materials, which would also contain abundant metallic iron remanence carriers, may be important anomaly sources, a possibility that is consistent with enhanced magnetic anomalies observed peripheral to SPA. The latter anomalies may be produced by amplified secondary ejecta impact shock waves in the thick SPA ejecta mantle occurring near the antipodes of the Imbrium and Serenitatis impacts. Together with converging seismic compressional waves, these antipodal impact shocks may have produced especially deep fracture zones along the northwest edge of SPA near the Imbrium antipode, allowing the ascent of magma with enhanced KREEP concentrations. Author Affiliation: (a) Lunar and Planetary Laboratory, University of Arizona, 1629 E. University Blvd., Tucson, AZ 85721, USA (b) Institute for Dynamics of Geospheres, Russian Academy of Sciences, Leninskii Prospect 38/6, 117334 Moscow, Russia (c) Planetary Science Institute, 1700 E. Ft. Lowell, Tucson, AZ 85719, USA Article History: Received 12 April 2007; Revised 7 August 2007

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.icarus.2007.04.025 Byline: Lon L. Hood (a), Nicola C. Richmond (a)(b), Keith P. Harrison (c), Robert J. Lillis (d) Keywords: Mars; Magnetic fields; Mars; interior; Mars; surface Abstract: Maps of the vector components of the martian crustal magnetic field over the strongly magnetized Terra Cimmeria/Sirenum region are constructed using Mars Global Surveyor magnetometer data. Although pronounced east-west trending anomalies are present on the radial and north field component maps at the mapping altitude ([approximately equal to]360-380 km), these trends are much less prominent at the lower aerobraking altitude ([approximately equal to]90-150 km). Comparisons with similar maps produced using artificial data at the aerobraking altitude indicate that elongated sources in this region may have maximum lengths along the martian surface of [approximately equal to]500 km and maximum aspect ratios of [approximately equal to]2. Iterative forward modeling of several relatively isolated anomalies in the mapped region yields paleomagnetic pole positions consistent with those estimated in previous studies of other anomalies using mapping phase and science phasing orbit data. On this basis, it is inferred that sources in the studied region are most probably magnetized primarily in northward or southward directions. Using this additional constraint, iterative forward modeling is then applied to determine a magnetization distribution that is consistent with data at both the aerobraking altitude and the mapping altitude. The model magnetization distribution, which includes 41 discrete sources, again indicates no highly elongated sources. An examination of surface geology in the region as well as a consideration of the global distribution of anomalies suggests that magmatic intrusions (e.g., subsurface dike swarms), cooling in the presence of water, are the most likely sources of the magnetic anomalies. Author Affiliation: (a) Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ 85721, USA (b) Planetary Science Institute, 1700 East Fort Lowell, Suite 106, Tucson, AZ 85719, USA (c) Southwest Research Institute, 1050 Walnut Street, Suite 400, Boulder, CO 80309, USA (d) Space Sciences Laboratory, University of California, Berkeley, CA 94720, USA Article History: Received 30 November 2006; Revised 11 April 2007

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.icarus.2005.02.008 Byline: Lon L. Hood (a), Corryn N. Young (a), Nicola C. Richmond (a), Keith P. Harrison (b) Keywords: Mars; magnetic fields; Mars; interior; Mars; surface Abstract: Maps of the vector components of the Mars crustal magnetic field are constructed at the mapping altitude (360 to 410 km) using a selected set of data obtained with the Mars Global Surveyor magnetometer during 2780 orbits of the planet in 1999. Forward modeling calculations are then applied to six relatively strong and isolated, dominantly dipolar, magnetic anomalies for the primary purpose of estimating bulk directions of magnetization. Assuming that the magnetizing field was a (dipolar) core dynamo field centered in the planet, paleomagnetic pole positions are calculated for the six primary source bodies together with that for a seventh anomaly analyzed earlier. In agreement with several previous studies, it is found that six of the seven pole positions are clustered in what is now the northern lowlands in a region centered northwest of Olympus Mons (mean pole position: 34[degrees][+ or -]10[degrees] N, 202[degrees][+ or -]58[degrees] E). Assuming that the dynamo dipole moment vector was approximately parallel to the rotation axis, the modeling results therefore suggest a major reorientation of Mars relative to its rotation axis after magnetization was acquired. Such a reorientation may have been stimulated by internal mass redistributions associated with the formation of the northern lowlands and Tharsis, for example. A comparison of the mean paleo (magnetic) equator to the global distribution of crustal fields shows that magnetic anomalies tend to occur at low paleolatitudes. The same appears to be true for the Noachian-aged valley networks, which exhibit a broad spatial correlation with the magnetic anomalies. A possible interpretation is that the formation of magnetic anomalies and the valley networks was favored in the tropics where melting of water ice and snow was a stronger source of both surface valley erosion and groundwater recharge during the earliest history of the planet. This would be consistent with models in which hydrothermal alteration of crustal rocks played a role in producing the unusually strong martian magnetic anomalies. Author Affiliation: (a) Lunar and Planetary Laboratory, University of Arizona, 1629 E. University Blvd., Tucson, AZ 85721-0092, USA (b) Southwest Research Institute, Boulder, CO 80309, USA Article History: Received 11 May 2004; Revised 9 February 2005

We present numerical simulations of the thermal and dynamical histories of solid particles (chondrules and their precursors--treated as 1-mm silicate spheres) during passage of an adiabatic shock wave through a particle-gas suspension in a minimum-mass solar nebula. The steady-state equations of energy, momentum, and mass conservation are derived and integrated for both solids and gas under a variety of shock conditions and particle number densities using the free-molecular-flow approximation. These simulations allow us to investigate both the heating and cooling of particles in a shock wave and to compare the time and distance scales associated with their processing to those expected for natural chondrules. The interactions with the particles cause the gas to achieve higher temperatures and pressures both upstream and downstream of the shock than would be reached otherwise. The cooling rates of the particles are found to be nonlinear but agree approximately with the cooling rates inferred for chondrules by laboratory simulations. The initial concentration of solids upstream of the shock controls the cooling rates and the distances over which they are processed: Lower concentrations cool more slowly and over longer distances. These simulations are consistent with the hypothesis that large-scale shocks, e.g., those due to density waves or gravitational instabilities, were the dominant mechanism for chondrule formation in the nebula. Key Words: meteorites; Solar System origin; solar nebula; thermal histories.

Numerical simulations aid the investigation of the reaction of a one dimensional radiative gas dynamic shock wave with a solar dust nebulae cloud. The numerical simulations involve the calculation of energy and momentum transfer to the shock-heated gas during gas penetration into the dust cloud. Grain heating caused by molecular interactions and rays from shocked gas are also obtained. The dust cloud is constituted by silicate grains of 1 millimeter radius.

Introduction: NASA designated Reiner Gamma as the destination for the first Payloads and Research Investigations on the Surface of the Moon (PRISM) delivery (known as PRISM-1a). Reiner Gamma (RG) is home to a magnetic anomaly, a region of magnetized crustal rocks. The RG magnetic anomaly, on the western nearside, is co-located with the type example of a class of unusual high-reflectance markings known as lunar swirls. PRISM payloads will be carried on commercial landers as part of NASA's Commercial Lunar Payload Services (CLPS) program. The RG lander and PRISM-1a payload are designed for operation during one lunar daylight period. NASA selected APL's Lunar Vertex proposal for the PRISM-1a mission in June of 2021. APL is providing overall management of Lunar Vertex, systems engineering, safety and mission assurance, two magnetometer instruments, and rover integration and testing. The Lunar Vertex Science Operations Center will be at APL. Lunar Vertex Goals: A lunar magnetic anomaly is a natural laboratory for addressing a wide range of questions in planetary science [e.g., 1, 2]. Lunar Vertex has the following goals: 1) Investigate the origin of lunar magnetic anomalies; 2) Investigate the origin of lunar swirls; 3) Determine the structure of the mini-magnetosphere that forms over the RG magnetic anomaly. These goals are traceable to the Planetary Decadal Survey [3] and other community guiding documents [4-7]. The mission goals will be accomplished by payload elements on the CLPS lander and on a Lunar Vertex rover. Lander Instruments: The lander suite includes three elements. The Vertex Camera Array (VCA) is a set of fixedmounted cameras. VCA images will be used to (a) survey landing site geology, and (b) perform photometric modeling of regolith characteristics. VCA is being built by Redwire Aerospace of Littleton, Co., USA. The Vector Magnetometer-Lander (VML) is a suite of fluxgate magnetometers. VML will operate during cruise and descent and on the surface to measure the in-situ magnetic field at multiple altitudes and through varying upstream conditions. Built by APL, VML has a dual ring-core fluxgate sensor mounted at the end of a mast. VML also has four commercial miniature magnetometers arrayed in a tetrahedron near the base of the mast. Gradiometry allows for separation of the natural field from that of the lander. The Magnetic Anomaly Plasma Spectrometer (MAPS) measures the energy, flux, and direction of ions and electrons that reach the surface. MAPS is provided by the Southwest Research Institute of San Antonio, Tx., USA. Rover. The CLPS lander will deploy the Lunar Vertex rover, which conducts a traverse reaching =500 m distance, obtaining measurements outside the zone disturbed by the lander rocket exhaust. Measurements of undisturbed regolith are key to testing hypotheses for the origin of swirls. Determination of the magnetic field strength and direction along the traverse will help to constrain the nature of the magnetic source. The rover provider is Lunar Outpost (Golden, Co., USA). Rover Instruments. The rover carries two instruments. The Rover Multispectral Microscope (RMM) will collect images at wavelengths ~0.37-0.94 µm using active LED illumination. RMM (from Canadensys Aerospace of Bolton, On., Canada) will reveal the composition, texture, and particle-size distribution of the regolith beneath the rover. The APL Vector Magnetometer-Rover (VMR) is a copy of a portion of VML: the array of four mini-magnetometers. VMR magnetic measurements will be correlated with changes in regolith properties documented by RMM. Lander Selection. In November 2021, NASA selected Intuitive Machines of Houston, Tx., USA as the provider of the CLPS lander that will deliver Lunar Vertex to the Moon. Launch is planned for April 2024. [ABSTRACT FROM AUTHOR]