366 research outputs found
Winds, B-Fields, and Magnetotails of Pulsars
We investigate the emission of rotating magnetized neutron stars due to the
acceleration and radiation of particles in the relativistic wind and in the
magnetotail of the star. We consider that the charged particles are accelerated
by driven collisionless reconnection. Outside of the light cylinder, the star's
rotation acts to wind up the magnetic field to form a predominantly azimuthal,
slowly decreasing with distance, magnetic field of opposite polarity on either
side of the equatorial plane normal to the star's rotation axis. The magnetic
field annihilates across the equatorial plane with the magnetic energy going to
accelerate the charged particles to relativistic energies. For a typical
supersonically moving pulsar, the star's wind extends outward to the standoff
distance with the interstellar medium. At larger distances, the power output of
pulsar's wind of electromagnetic field and relativistic particles
is {\it redirected and collimated into the magnetotail} of the star. In the
magnetotail it is proposed that equipartition is reached between the magnetic
energy and the relativistic particle energy. For such conditions, synchrotron
radiation from the magnetotails may be a significant fraction of
for high velocity pulsars. An equation is derived for the radius of the
magnetotail as a function of distance from the star.
For large distances , of the order of the distance travelled by the
star, we argue that the magnetotail has a `trumpet' shape owing to the slowing
down of the magnetotail flow.Comment: 11 pages, 4 figures, accepted for publication in Ap
Simultaneous, in situ measurements of OH, HO_2, O_3, and H_2O: A test of modeled stratospheric HO_x chemistry
Simultaneous, in situ measurements of OH, HO_2, H_2O, and O_3 from 37â23 km are reported. The partitioning between OH and HO_2 and the total HO_x concentration are compared with expected steady-state values. The ratio of HO_2 to OH varies from less than 2 at 36 km to more than 3 at 25 km; in the lower stratosphere this ratio is nearly a factor of two less than predicted. The data are used to calculate HO_x production and loss rates. The measured HOx mixing ratio is consistent with production dominated by the reaction of O(1D) with H_2O, and loss controlled by NO_y below 28 km and HO_x above 30 km. The steady-state concentration of H_2O_2 is inferred from the measured HO_2 concentration and calculated photolysis rate. The maximum H_2O_2 mixing ratio (at 33 km) is predicted to be less than 0.2 ppb
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Short-term variability of solar wind number density, speed and dynamic pressure as a function of the interplanetary magnetic field components: A survey over two solar cycles
The variability of hourly values of solar wind number density, number density variation, speed, speed variation and dynamic pressure with IMF Bz and magnitude |B| has been examined for the period 1965â1986. We wish to draw attention to a strong correlation in number density and number density fluctuation with IMF Bz characterised by a symmetric increasing trend in these quantities away from Bz = 0 nT. The fluctuation level in solar wind speed is found to be relatively independent of Bz. We infer that number density and number density variability dominate in controlling solar wind dynamic pressure and dynamic pressure variability. It is also found that dynamic pressure is correlated with each component of IMF and that there is evidence of morphological differences between the variation with each component. Finally, we examine the variation of number density, speed, dynamic pressure and fluctuation level in number density and speed with IMF magnitude |B|. Again we find that number density variation dominates over solar wind speed in controlling dynamic pressure
A New Model of Jupiter's Magnetic Field from Juno's First Nine Orbits
A spherical harmonic model of the magnetic field of Jupiter is obtained from vector magnetic field observations acquired by the Juno spacecraft during its first nine polar orbits about the planet. Observations acquired during eight of these orbits provide the first truly global coverage of Jupiter's magnetic field with a coarse longitudinal separation of ~45 deg between perijoves. The magnetic field is represented with a degree 20 spherical harmonic model for the planetary ("internal") field, combined with a simple model of the magnetodisc for the field ("external") due to distributed magnetospheric currents. Partial solution of the underdetermined inverse problem using generalized inverse techniques yields a model ("Juno Reference Model through Perijove 9") of the planetary magnetic field with spherical harmonic coefficients well determined through degree and order 10, providing the first detailed view of a planetary dynamo beyond Earth
Consequences of a saturated convection electric field on the ring current
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/94778/1/grl15466.pd
Origins of the Ambient Solar Wind: Implications for Space Weather
The Sun's outer atmosphere is heated to temperatures of millions of degrees,
and solar plasma flows out into interplanetary space at supersonic speeds. This
paper reviews our current understanding of these interrelated problems: coronal
heating and the acceleration of the ambient solar wind. We also discuss where
the community stands in its ability to forecast how variations in the solar
wind (i.e., fast and slow wind streams) impact the Earth. Although the last few
decades have seen significant progress in observations and modeling, we still
do not have a complete understanding of the relevant physical processes, nor do
we have a quantitatively precise census of which coronal structures contribute
to specific types of solar wind. Fast streams are known to be connected to the
central regions of large coronal holes. Slow streams, however, appear to come
from a wide range of sources, including streamers, pseudostreamers, coronal
loops, active regions, and coronal hole boundaries. Complicating our
understanding even more is the fact that processes such as turbulence,
stream-stream interactions, and Coulomb collisions can make it difficult to
unambiguously map a parcel measured at 1 AU back down to its coronal source. We
also review recent progress -- in theoretical modeling, observational data
analysis, and forecasting techniques that sit at the interface between data and
theory -- that gives us hope that the above problems are indeed solvable.Comment: Accepted for publication in Space Science Reviews. Special issue
connected with a 2016 ISSI workshop on "The Scientific Foundations of Space
Weather." 44 pages, 9 figure
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Ozone climatology using interactive chemistry: results from the Canadian Middle Atmosphere Model
The climatology of ozone produced by the Canadian Middle Atmosphere Model (CMAM) is presented. This three-dimensional global model incorporates the radiative feedbacks of ozone and water vapor calculated on-line with a photochemical module. This module includes a comprehensive gas-phase reaction set and a limited set of heterogeneous reactions to account for processes occurring on background sulphate aerosols. While transport is global, photochemistry is solved from about 400 hPa to the top of the model at âŒ95 km. This approach provides a complete and comprehensive representation of transport, emission, and photochemistry of various constituents from the surface to the mesopause region. A comparison of model results with observations indicates that the ozone distribution and variability are in agreement with observations throughout most of the model domain. Column ozone annual variation is represented to within 5â10% of the observations except in the Southern Hemisphere for springtime high latitudes. The vertical ozone distribution is generally well represented by the model up to the mesopause region. Nevertheless, in the upper stratosphere, the model generally underestimates the amount of ozone as well as the latitudinal tilting of ozone isopleths at high latitude. Ozone variability is analyzed and compared with measurements. The comparison shows that the phase and amplitude of the seasonal variation as well as shorter timescale variations are well represented by the model at various latitudes and heights. Finally, the impact of incorporating ozone radiative feedback on the model climatology is isolated. It is found that the incorporation of ozone radiative feedback results in a cooling of âŒ8 K in the summer stratopause region, which corrects a warm bias that results when climatological ozone is used
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