2,336 research outputs found
Thunderstorm/environment interactions that affect subsequent convection
Mesoscale kinematics and thermodynamics of severe thunderstorm-baroclinic zone interactions, and the development and evolution of mesoscale pressure systems associated with strong convective storms, are being studied in an ongoing research project
Interactions Between Convective Storms and Their Environment
The ways in which intense convective storms interact with their environment are considered for a number of specific severe storm situations. A physical model of subcloud wind fields and vertical wind profiles was developed to explain the often observed intensification of convective storms that move along or across thermal boundaries. A number of special, unusually dense, data sets were used to substantiate features of the model. GOES imagery was used in conjunction with objectively analyzed surface wind data to develop a nowcast technique that might be used to identify specific storm cells likely to become tornadic. It was shown that circulations associated with organized meso-alpha and meso-beta scale storm complexes may, on occasion, strongly modify tropospheric thermodynamic patterns and flow fields
Redshifts in the Southern Abell Redshift Survey Clusters. I. The Data
The Southern Abell Redshift Survey contains 39 clusters of galaxies with
redshifts in the range 0.0 < z < 0.31 and a median redshift depth of z =
0.0845. SARS covers the region 0 21h (while
avoiding the LMC and SMC) with b > 40. Cluster locations were chosen from the
Abell and Abell-Corwin-Olowin catalogs while galaxy positions were selected
from the Automatic Plate Measuring Facility galaxy catalog with
extinction-corrected magnitudes in the range 15 <= b_j < 19. SARS utilized the
Las Campanas 2.5 m duPont telescope, observing either 65 or 128 objects
concurrently over a 1.5 sq deg field. New redshifts for 3440 galaxies are
reported in the fields of these 39 clusters of galaxies.Comment: 20 pages, 5 figures, accepted for publication in the Astronomical
Journal, Table 2 can be downloaded in its entirety from
http://trotsky.arc.nasa.gov/~mway/SARS1/sars1-table2.cs
Cassiopeia A: dust factory revealed via submillimetre polarimetry
If Type-II supernovae - the evolutionary end points of short-lived, massive
stars - produce a significant quantity of dust (>0.1 M_sun) then they can
explain the rest-frame far-infrared emission seen in galaxies and quasars in
the first Gyr of the Universe. Submillimetre observations of the Galactic
supernova remnant, Cas A, provided the first observational evidence for the
formation of significant quantities of dust in Type-II supernovae. In this
paper we present new data which show that the submm emission from Cas A is
polarised at a level significantly higher than that of its synchrotron
emission. The orientation is consistent with that of the magnetic field in Cas
A, implying that the polarised submm emission is associated with the remnant.
No known mechanism would vary the synchrotron polarisation in this way and so
we attribute the excess polarised submm flux to cold dust within the remnant,
providing fresh evidence that cosmic dust can form rapidly. This is supported
by the presence of both polarised and unpolarised dust emission in the north of
the remnant, where there is no contamination from foreground molecular clouds.
The inferred dust polarisation fraction is unprecedented (f_pol ~ 30%) which,
coupled with the brief timescale available for grain alignment (<300 yr),
suggests that supernova dust differs from that seen in other Galactic sources
(where f_pol=2-7%), or that a highly efficient grain alignment process must
operate in the environment of a supernova remnant.Comment: In press at MNRAS, 10 pages, print in colou
A Study of Compact Radio Sources in Nearby Face-on Spiral Galaxies. II. Multiwavelength Analyses of Sources in M51
We report the analysis of deep radio observations of the interacting galaxy
system M51 from the Very Large Array, with the goal of understanding the nature
of the population of compact radio sources in nearby spiral galaxies. We detect
107 compact radio sources, 64% of which have optical counterparts in a deep
H Hubble Space Telescope image. Thirteen of the radio sources have
X-ray counterparts from a {\em Chandra} observation of M51. We find that six of
the associated H sources are young supernova remnants with resolved
shells. Most of the SNRs exhibit steep radio continuum spectral indices
onsistent with synchrotron emission. We detect emission from the Type Ic SN
1994I nearly a decade after explosion: the emission (Jy
beam at 20 cm, Jy beam at 6cm,
) is consistent with light curve models for Type Ib/Ic
supernovae. We detect X-ray emission from the supernova, however no optical
counterpart is present. We report on the analysis of the Seyfert 2 nucleus in
this galaxy, including the evidence for bipolar outflows from the central black
hole.Comment: 22 pages, 8 figures (5 color) in separate files, AASTeX. Full
resolution figures and preprint may be obtained by contacting
[email protected]. AJ accepte
Diurnal Distribution of Very Heavy Precipitation Over the Central and Eastern United States
A climatology of heavy precipitation events for the states of Nebraska, Missouri, Illinois, Kentucky, Tennessee, West Virginia, Pennsylvania, and Virginia is developed from 10 years (1968-1977) of Hourly Precipitation Data. Hourly precipitation events are categorized by severity, ranging from 1 to 2 inches (2.5 to 5.1 cm) in one hour or less (Type 1) to 4 or more inches (greater than 10.2 cm) in eight hours or less (Type 4). Hourly distributions of heavy precipitation events indicate that intense rainfalls of short duration occur most frequently during the afternoon and evening hours; whereas Type 4 events, which pose the most serious threat of flash flooding occur most often during the night and early morning hours in the central and eastern United States
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