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ALMA Detection of a Linearly Polarized Reverse Shock in GRB 190114C
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Defining the Polar Field Reversal
The polar fields on the Sun are directly related to solar cycle variability. Recently there has been interest in studying an important characteristic of the polar fields: the timing of the polar field reversals. However this characteristic has been poorly defined, mostly due to the limitations of early observations. In the past, the reversals have been calculated by averaging the flux above some latitude (i.e. 55deg or 75deg). Alternatively, the reversal could be defined by the time in which the previous polarity is completely canceled and replaced by the new polarity at 90de, precisely at the pole. We will use a surface flux transport model to illustrate the differences in the timing of the polar field reversal based on each of these definitions and propose standardization in the definition of the polar field reversal. The ability to predict the timing of the polar field reversal using a surface flux transport model will also be discussed.
The dependence of solar modulation on the sign of the cosmic ray particle charge
ISEE-3 spacecraft cosmic ray telescope data on the modulation of cosmic ray electrons are compared with IMP-8 spacecraft data on low energy He atoms to evaluate the effects of solar maxima on cosmic ray modulation. The investigation is constrained to the modulation of 70-95 MeV He-4 nuclei and 600-1000 MeV electrons over the period 1965-1984, an interval covering solar maxima in 1970 and 1981. It is shown that the occurrences of solar maxima are associated with magnetic field polarity reversals. When the interplanetary magnetic field reverses polarity, oppositely charged particles flow in different directions, thereby permitting studies of drift effects and modulation. Data on the recovery periods after the solar maxima show that the He-4 nuclei recovered before the electron population in 1970, while the situation was reversed in 1981. Actual flux ratio reversals were recorded in the years surrounding the maxima. Although the data support a connection between modulation of cosmic rays and the sign of charged particles, current models cannot account for the deviation of electron intensities from the nuclei intensities.
Coronal Polarization of Pseudostreamers and the Solar Polar Field Reversal
The reversal of the solar polar magnetic field is notoriously hard to pin down due to the extreme viewing angle of the pole. In Cycle 24, the southern polar field reversal can be pinpointed with high accuracy due to a large-scale pseudostreamer that formed over the pole and persisted for approximately a year. We tracked the size and shape of this structure with multiple observations and analysis techniques including PROBA2/SWAP EUV images, AIA EUV images, CoMP polarization data, and 3D tomographic reconstructions. We find that the heliospheric field reversed polarity in February 2014, whereas in the photosphere, the last vestiges of the previous polar field polarity remained until March 2015. We present here the evolution of the structure and describe its identification in the Fe XII 1074nm coronal emission line, sensitive to the Hanle effect in the corona.
The heliospheric current sheet - 3-dimensional structure and solar cycle changes
The reversal in polarity of the interplanetary current sheet/sector structure is investigated during the recent solar maximum. Multipoint observations by ISEE-3 and Pioneer 11 show that a simple two sector or occasional four sector structure persisted throughout the maximum and out to distances of 10 AU. The polarity reversal occurred between March 1979 and October 1980, without any indication of an abrupt transition that might permit a more precise timing. The reversal coincided approximately with the reversal in the sun's polar cap fields. The current sheet appeared to be highly inclined during the ascending and descending phases of the solar cycle but was apparently too complex to describe as a simple inclined current sheet during solar maximum.
Observations of the reappearance of polar coronal holes and the reversal of the polar magnetic field
Observational data relating to the evolution of the polar magnetic field around sunspot maximum is examined. Particular emphasis is given to coronal hole observations performed during the last two solar maxima. Long-term averages of the latitudinal dependence of the photospheric magnetic field and the evolutionary pattern of the polar crown filaments are used to trace the poleward motion of the reversal of the large-scale field and are compared to the redevelopment of polar holes. Within the context of phenomenological models of the solar cycle, it is concluded that: (1) the process of polarity reversal and redevelopment of polar holes is discontinuous, with surges of flux of old-cycle polarity interrupting the poleward migration of new-cycle flux; (2) contrary to the Babcock (1961) hypothesis, the polar crown disappears months after the magnetic pole reversal; and (3) the observations support suggestions of a poleward meridional flow around solar maximum that cannot be accounted for by Leighton-type (1964) diffusion.
Origin of the Sheared Magnetic Fields that Erupt in Flares and Coronal Mass Ejections
From a search of the Yohkoh/SXT whole-Sun movie in the years 2000 and 2001, we found 37 flare-arcade events for which there were full-disk magnetograms from SOHO/MDI, coronagraph movies from SOHO/LASCO, and before and after full-disk chromospheric images from SOHOBIT and/or from ground-based observatories. For each event, the observations show or strongly imply that the flare arcade was produced in the usual way by the eruption of sheared core field (as a flux rope) from along the neutral line inside a mature bipolar magnetic arcade. Two-thirds (25) of these arcades had the normal leading-trailing magnetic polarity arrangement of the active regions in the hemisphere of the arcade, but the other third (12) had reversed polarity, their leading flux being the trailing-polarity remnant of one or more old active regions and their trailing flux being the leading-polarity remnant of one or more other old active regions. From these observations, we conclude: (1) The sheared core field in a reversed-polarity arcade must be formed by processes in and above the photosphere, not by the emergence of a twisted flux rope bodily from below the photosphere. (2) The sheared core fields in the normal-polarity arcades were basically the same as those in the reversed-polarity arcades: both showed similar sigmoidal form and produced similar explosions (similar flares and CMEs). (3) Hence, the sheared core fields in normal-polarity mature arcades are likely formed mainly by the same processes as in reversed-polarity arcades. (4) These processes should be discernible in high-resolution magnetogram sequences and movies of the photosphere, chromosphere, and corona such those to come from Solar-B
Paleomagnetism and Tectonic Interpretations of the Taos Plateau Volcanic Field, Rio Grande Rift, New Mexico
The tectonic response of the Taos Plateau volcanic field in the southern San Luis basin to the late stage extensional environment of the Rio Grande rift was investigated using paleomagnetic techniques. Sixty-two sites (533 samples) of Pliocene volcanic units were collected covering four major rock types with ages of 4.7 to 1.8 Ma. Twenty-two of these sites were from stratigraphic sections of the lower, middle and upper Servilleta Basalt collected in the Rio Grande gorge at two locations 19 km apart. Flows from the lower and middle members in the southern gorge record reversed polarities, while those in Garapata Canyon are normal with an excursion event in the middle of the sequence. The uppermost flows of the upper member at both sites display normal directions. Although these sections correlate chemically, they seem to represent different magnetic time periods during the Gilbert Reversed-Polarity Chiron. Alternating field demagnetization, aided by principal component analysis, yields 55 sites with stable directions representing both normal and reversed polarities, and five sites indicating transitional fields. Mean direction of the normal and inverted reversed sites is I=49.3 deg. and D=356.7 deg. (alpha(sub 95)=3.6 deg). Angular dispersion of the virtual geomagnetic poles is 16.3 deg, which is consistent with paleosecular variation model G, fit to data from the past 5 m.y. Comparison with the expected direction indicates no azimuthal rotation of the Taos Plateau volcanic field; inclination flattening for the southern part of the plateau is 8.3 deg +/- 5.3 deg. Previous paleomagnelic data indicate 10 deg- 15 deg counterclockwise rotation of die Espanola block to the south over the past 5 m.y. The data suggest the Taos Plateau volcanic field, showing no rotation and some flattening in the south and east, has acted as a stable buttress and has been downwarped by overriding of the southeastern end of the plateau by the Picuris Mountains, which make up the northern corner of the counterclockwise rotating Espanola block.
The keyhole region in VPPA welds
The morphology and properties of the Variable Polarity Plasma Arc (VPPA) weld composite zone are intimately related to the physical processes associated with the keyhole. The effects of microsegregation and transient weld stress on macrosegregation in the weld tool are examined. In addition the electrical character of straight and reverse polarity portions of the arc cycle were characterized. The results of the former study indicate that alloy 2219 is weldable because large liquid volumes are available during latter stages of weld solidification. Strains in the pool region, acting in conjunction with weld microsegregation can produce macrosegregation great enough to produce radiographic contrast effects in welds. Mechanisms of surface copper enrichment were identified. The latter study has demonstrated that increased heat is delivered to workpieces if the reverse polarity proportion of the weld cycle is increased. Current in the straight polarity portion of the welding cycle increased as the reverse cycle proportion increased. Voltage during reverse polarity segments is large.
Alternating-Polarity Arc Welding
Brief reversing polarity of welding current greatly improves quality of welds. NASA technical memorandum recounts progress in art of variable-polarity plasma-arc (VPPA) welding, with emphasis on welding of aluminum-alloy tanks. VPPA welders offer important advantages over conventional single-polarity gas/tungsten arc welders.
Two-polarity magnetization in the Manson impact breccia
A preliminary paleomagnetic study of the impact breccia matrix and clasts has produced surprising results--nearly antipodal normal and reversed polarity magnetic vectors are observed in different portions of the core. Near-antipodal magnetizations within a segment of matrix and within individual samples rule out core inversion as the explanation of the dual polarity. In both the dense and the sandy matrix breccias, the magnetizations of clasts and matrix within the same core segment are identical; this negative 'conglomerate test' indicates that magnetization originated after impact. Paleomagnetic study of the Manson Impact Structure is an attempt to refine the Ar-40/Ar-39 age (65.7 +/- 1 m.y.) that suggests Manson to be a Cretaceous-Tertiary boundary impact. Refinement is possible because the boundary occurs within a reversed polarity interval (29R) of only 0.5 m.y. duration. The two breccia types in the Manson structure were both examined: one of a very dense matrix and apparently partially melted, and the breccia stratigraphically below it of granular or 'sandy' chloritic matrix. Samples were taken from the matrixes and a wide variety of clast compositions, including granite, diabase, gneiss, amphibolite, and melted granite. Currently, measurements have been made on 22 samples, using 30-35 steps of either alternating field (AF) or thermal demagnetization.
Unusual Polar Conditions in Solar Cycle 24 and Their Implications for Cycle 25
We report on the prolonged solar-maximum conditions until late 2015 at the north-polar region of the Sun indicated by the occurrence of high-latitude prominence eruptions (PEs) and microwave brightness temperature close to the quiet-Sun level. These two aspects of solar activity indicate that the polarity reversal was completed by mid-2014 in the south and late 2015 in the north. The microwave brightness in the south-polar region has increased to a level exceeding the level of the Cycle 23/24 minimum, but just started to increase in the north. The northsouth asymmetry in the polarity reversal has switched from that in Cycle 23. These observations lead us to the hypothesis that the onset of Cycle 25 in the northern hemisphere is likely to be delayed with respect to that in the southern hemisphere. We find that the unusual condition in the north is a direct consequence of the arrival of poleward surges of opposite polarity from the active region belt. We also find that multiple rush-to-the-pole episodes were indicated by the PE locations that lined up at the boundary between opposite-polarity surges. The high-latitude PEs occurred in the boundary between the incumbent polar flux and the insurgent flux of opposite polarity.
Effect of a longitudinally applied voltage upon the growth of Zea mays seedlings
The electrical parameters that affect young seedling growth were investigated. Voltages ranging from 5 to 40 volts were applied longitudinally along the mesocotyl region of 4-day old Zea mays L. (cv Silver Queen) seedlings for periods of 3 or 4 hours. It was determined that: (a) making the tips of the seedlings electrically positive relative to the base strongly inhibited shoot growth at 5 volts, whereas the reverse polarity had no effect; (b) at higher voltages, making the tip of the seedlings negative caused less growth inhibition than the reverse polarity at each voltage level; (c) the higher the applied voltage the greater the degree of inhibition; and, (d) the more growth inhibition experienced by the plants the poorer, and slower, their recovery. Previous observations of a relationship between the amount of free indole-3-acetic acid in the mesocotyl cortex and the growth rate of the mesocotyl and of gravitropism-induced movement of labeled indole-3-acetic acid from the seed to the shoot lead to the prediction of a voltage-dependent gating of the movement of indole-3-acetic acid from the stele to the cortex. This provided the basis for attempting to alter the growth rate of seedlings by means of an applied voltage.
The cause of two plasma-tail disconnection events in comet P/Haley during the ICE-Halley radial period
The causes of two plasma-tail disconnection events (DEs), which occurred in Halley's comet on March 20-22 and April 11-12, 1986, during the ICE-Halley radial period, are analyzed using the ICE magnetometer and electron plasma data. It is concluded that the DE of March 20-22 was most likely caused by an IMF polarity reversal. The DE of April 11-12 on the other hand, is attributed to either a compression region in the solar wind, an IMF polarity reversal, or a combination of the two. Assuming that the two DEs are due to frontside reconnection after an IMF reversal, it was estimated that the time period between the onset of reconnection and the final disconnection of the tail is between 0.1 and 0.6 day, suggesting that the average speed at which reconnection proceeds through the cometary magnetic field pile-up region is between 1 and 6 km/sec, or several tenths of the local Alfven speed.
Drift and observations in cosmic-ray modulation, 2
The significant effect of drift on the radial and latitudinal dependence of cosmic rays for consecutive solar minimum periods is illustrated. Compared with the integral radial gradient observed in 1976, the calculated value seems too small. A detailed comparison will however have to await the forthcoming solar minimum. The same applies to the latitudinal gradient which is as yet inconclusive about drift effects. Searching the literature for observations related to the IMF polarity reversal, distinct differences were found in neutron monitor response functions for consecutive solar minimum periods, and also in the annual variations of cosmic rays observed before and after polarity reversals. Whether drift is the predominant effect is however not yet clear. Better correlation was found between variations in the cosmic ray intensity and solar activity parameters over a much wider range of heliolatitude during 1970-80 compared to before this period.
Paleomagnetism and tectonic interpretations of the Taos Plateau volcanic field, Rio Grande rift, New Mexico
The tectonic response of the Taos Plateau volcanic field in the southern San Luis basin to late stage extensional environment of the Rio Grande rift was investigate using paleomagnetic techniques. Sixty-two sites (533 samples) of Pliocene volcanic units were collected covering four major rock types with ages of 4.7 to 1.8 Ma. Twenty-two of these sites were from stratigraphic sections of the lower, middle and upper Servilleta Basalt collected in the Rio Grande gorge at two locations 19 km apart. Flows from the lower and middle members in the southern gorge record reversed polarities, while those in Garapata Canyon are normal with an excursion event in the middle of the sequence. The uppermost flows of the upper member at both sites display normal directions. Although these sections correlate chemically, they seem to represent different magnetic time periods during the Gilbert Reversed-Polarity Chron. The data suggest the Taos Plateau volcanic field, showing no rotation and some flattening in the south and east, has acted as a stable buttress and has been downwarped by overriding of the southeastern end of the plateau by the Picuris Mountains, which make up the northern corner of the counter-clockwise rotating Espanola block.
Paleomagnetism and Tectonic Interpretations of the Taos Plateau Volcanic Field, Rio Grande Rift, New Mexico
The tectonic response of the Taos Plateau volcanic field in the southern San Luis basin to the late stage extensional environment of the Rio Grande rift was investigated using paleomagnetic techniques. Sixty-two sites (533 samples) of Pliocene volcanic units were collected covering four major rock types with ages of 4.7 to 1.8 Ma. Twenty-two of these sites were from stratigraphic sections of the lower, middle and upper Servilleta Basalt collected in the Rio Grande gorge at two locations 19 km apart. Flows from the lower and middle members in the southern gorge record reversed polarities while those in Garapata Canyon are normal with an excursion event in the middle of the sequence. The uppermost flows of the upper member at both sites display normal directions. Although these sections correlate chemically, they seem to represent different magnetic time periods during the Gilbert Reversed-Polarity Chron...