322 research outputs found
Some problems in coupling solar activity to meteorological phenomena
The development of a theory of coupling of solar activity to meteorological phenomena is hindered by the difficulties of devising a mechanism that can modify the behavior of the troposphere while employing only a negligible amount of energy compared with the energy necessary to drive the normal meteorological system, and determining how such a mechanism can effectively couple some relevant magnetospheric process into the troposphere in such a way as to influence the weather. A clue to the nature of the interaction between the weather and solar activity might be provided by the fact that most solar activity undergoes a definite 11-yr cycle, and meteorological phenomena undergo either no closely correlated variation, an 11-yr variation, or a 22-yr variation
Evidence for short cooling time in the Io plasma torus
We present empirical evidence for a radiative cooling time for the Io plasma torus that is about a factor of ten less than presently accepted values. We show that brightness fluctuations of the torus in the extreme ultraviolet (EUV) at one ansa are uncorrelated with the brightness at the other ansa displaced in time by five hours, either later or earlier. Because the time for a volume of plasma to move from one ansa to the other is only five hours, the cooling time must be less than this transport time in order to wipe out memory of the temperatures between ansae. Most (âŒ80â85%) of the EUV emission comes from a narrow (presumably ribbonâlike) feature within the torus. The short cooling time we observe is compatible with theoretical estimates if the electron density in the ribbon is âŒ10^4/cm^3. The cooling time for the rest of the torus (which radiates the remaining 15â20% of the power) is presumably consistent with the previously derived 20âhour values. A nearlyâcontinuous heating in both longitude and time is needed to maintain the EUV visibility of the torus ribbonâa requirement not satisfied by presently available theories
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
Trajectory model simulations of ozone (O<sub>3</sub>) and carbon monoxide (CO) in the lower stratosphere
A domain-filling, forward trajectory model originally developed for
simulating stratospheric water vapor is used to simulate ozone (O3) and
carbon monoxide (CO) in the lower stratosphere. Trajectories are
initialized in the upper troposphere, and the circulation is based on
reanalysis wind fields. In addition, chemical production and loss rates
along trajectories are included using calculations from the Whole Atmosphere
Community Climate Model (WACCM). The trajectory model results show good
overall agreement with satellite observations from the Aura Microwave Limb
Sounder (MLS) and the Atmospheric Chemistry Experiment Fourier Transform
Spectrometer (ACE-FTS) in terms of spatial structure and seasonal
variability. The trajectory model results also agree well with the Eulerian
WACCM simulations. Analysis of the simulated tracers shows that seasonal
variations in tropical upwelling exerts strong influence on O3 and CO
in the tropical lower stratosphere, and the coupled seasonal cycles provide
a useful test of the transport simulations. Interannual variations in the
tracers are also closely coupled to changes in upwelling, and the trajectory
model can accurately capture and explain observed changes during 2005â2011.
This demonstrates the importance of variability in tropical upwelling in
forcing chemical changes in the tropical lower stratosphere
The Jovian hydrogen bulge: Evidence for co-rotating magnetospheric convection
The hydrogen bulge is a feature in Jupiter's upper atmosphere that co-rotates with the planetary magnetic field (i.e. the hydrogen bulge is fixed in System III coordinates). It is located approximately 180[deg] removed in System III longitude from the active sector, which has been identified as the source region for Jovian decametric radio emission and for release of energetic electrons into interplanetary space. According to the magnetic-anomaly model, the active sector is produced by the effect of the large magnetic anomaly in Jupiter's northern hemisphere. On the basis of the magnetic-anomaly model, it has been theoretically expected for some time that a two-cell magnetospheric convection pattern exists within the Jovian magnetosphere. Because the convection pattern is established by magnetic-anomaly effects of the active sector, the pattern co-rotates with Jupiter. (This is in contrast to the Earth's two-cell convection pattern that is fixed relative to the Sun with the Earth rotating beneath it.) The sense of the convection is to bring hot magnetospheric plasma into the upper atmosphere in the longitude region of the hydrogen bulge. This hot plasma contains electrons with energies of the order of 100keV that dissociate atmospheric molecules to produce the atomic hydrogen that creates the observed longitudinal asymmetry in hydrogen Lyman alpha emission. We regard the existence of the hydrogen bulge as the best evidence available thus far for the reality of the expected co-rotating magnetospheric convection pattern.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/24466/1/0000741.pd
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
Morphology and time variability of Io's visible aurora
Clear-filter imaging of Io during the Galileo nominal and extended missions recorded diffuse auroral emissions in 16 distinct observations taken during 14 separate eclipses over a two year period. These images show that the morphology and time variability of the visible aurora have several similarities to Io's far ultraviolet emissions. The orbital leading hemisphere of Io is consistently brighter than the trailing hemisphere, probably due to a greater concentration of torus electrons in the wake region of the satellite. The locations of the polar limb glow and the bright equatorial glows appear to correlate with Io's System III longitude. Unlike the far ultraviolet emissions, the visible aurorae are enhanced near actively venting volcanic plumes, probably because of molecular emission by SO_2
Bulk Properties of Isentropic Mixing into the Tropics in the Lower Stratosphere
Timescales for mixing of midlatitude air into the tropical lower stratosphere are deduced from observations of long-lived tracers N2O and CCl3F. Bulk mixing between tropical and midlatitude regions is assumed to be isentropic and relatively slow compared with local mixing within each region. The mean value of the mixing timescale ranges from 12 to 18 months near 20 km. There is a tendency for shorter mixing times at higher and lower altitudes, although vertical profiles of mixing cannot be definitively established by the data. A more robust quantity is given by the fraction of midlatitude air entrained into the tropical upwelling region. Implied mixing fractions exceed 50% above 22 km
The impact of temperature vertical structure on trajectory modeling of stratospheric water vapor
Lagrangian trajectories driven by reanalysis meteorological fields are
frequently used to study water vapor (H2O) in the stratosphere, in which
the tropical cold-point temperatures regulate the amount of H2O entering
the stratosphere. Therefore, the accuracy of temperatures in the tropical
tropopause layer (TTL) is of great importance for understanding stratospheric
H2O abundances. Currently, most reanalyses, such as the NASA MERRA
(Modern Era Retrospective â analysis for Research and Applications), only
provide temperatures with ~ 1.2 km vertical resolution in the TTL,
which has been argued to miss finer vertical structure in the tropopause and
therefore introduce uncertainties in our understanding of stratospheric
H2O. In this paper, we quantify this uncertainty by comparing the
Lagrangian trajectory prediction of H2O using MERRA temperatures on
standard model levels (traj.MER-T) to those using GPS temperatures
at finer vertical resolution (traj.GPS-T), and those using adjusted
MERRA temperatures with finer vertical structures induced by waves
(traj.MER-Twave). It turns out that by using temperatures with finer
vertical structure in the tropopause, the trajectory model more realistically
simulates the dehydration of air entering the stratosphere. But the effect on
H2O abundances is relatively minor: compared with traj.MER-T,
traj.GPS-T tends to dry air by ~ 0.1 ppmv, while
traj.MER-Twave tends to dry air by 0.2â0.3 ppmv. Despite these
differences in absolute values of predicted H2O and vertical dehydration
patterns, there is virtually no difference in the interannual variability in
different runs. Overall, we find that a tropopause temperature with finer
vertical structure has limited impact on predicted stratospheric H2O
The impact of temperature vertical structure on trajectory modeling of stratospheric water vapor
Lagrangian trajectories driven by reanalysis meteorological fields are
frequently used to study water vapor (H<sub>2</sub>O) in the stratosphere, in which
the tropical cold-point temperatures regulate the amount of H<sub>2</sub>O entering
the stratosphere. Therefore, the accuracy of temperatures in the tropical
tropopause layer (TTL) is of great importance for understanding stratospheric
H<sub>2</sub>O abundances. Currently, most reanalyses, such as the NASA MERRA
(Modern Era Retrospective â analysis for Research and Applications), only
provide temperatures with ~ 1.2 km vertical resolution in the TTL,
which has been argued to miss finer vertical structure in the tropopause and
therefore introduce uncertainties in our understanding of stratospheric
H<sub>2</sub>O. In this paper, we quantify this uncertainty by comparing the
Lagrangian trajectory prediction of H<sub>2</sub>O using MERRA temperatures on
standard model levels (<i>traj.MER-T</i>) to those using GPS temperatures
at finer vertical resolution (<i>traj.GPS-T</i>), and those using adjusted
MERRA temperatures with finer vertical structures induced by waves
(<i>traj.MER-Twave</i>). It turns out that by using temperatures with finer
vertical structure in the tropopause, the trajectory model more realistically
simulates the dehydration of air entering the stratosphere. But the effect on
H<sub>2</sub>O abundances is relatively minor: compared with <i>traj.MER-T</i>,
<i>traj.GPS-T</i> tends to dry air by ~ 0.1 ppmv, while
<i>traj.MER-Twave</i> tends to dry air by 0.2â0.3 ppmv. Despite these
differences in absolute values of predicted H<sub>2</sub>O and vertical dehydration
patterns, there is virtually no difference in the interannual variability in
different runs. Overall, we find that a tropopause temperature with finer
vertical structure has limited impact on predicted stratospheric H<sub>2</sub>O
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