180 research outputs found
Tornadogenesis And Tornadogenesis Failure In Numerically Simulated Supercells
Simulations were performed in an idealized cloud model to study the processes responsible for tornadogenesis and tornadogenesis failure. The simulations were initialized with supercell proximity soundings taken from the Rapid Update Cycle (RUC) model. Because of the large number of simulations performed, several objective techniques were developed and tested to assist in the simulations--including automated supercell and tornado detection. In addition, the vast majority of the RUC soundings contained capping inversions, and thus the traditional `warm bubble\u27 convective initiation technique was unsuccessful. A new sustained convective initiation technique was tested to determine which configuration produced the strongest, longest-lived supercells.
Twenty-one tornadic simulations were examined. It was found that 0-3 km storm relative environmental helicity was the best predictor of the intensity (i.e. maximum pressure drop) and duration of the simulated tornadoes. A trajectory analysis found that vertical vorticity was generated in rising parcels as they ascended towards the tornado, and also by parcels that descended from aloft. However, large positive vertical vorticity was only produced after the parcels reached the surface. The most striking difference between the tornadic and nontornadic simulations was that the tornadic simulations produced more negative vertical vorticity in descending parcels, and that the parcels that entered the low-level circulation rose to higher altitudes than the parcels in the nontornadic simulations
Black hole quasinormal modes using the asymptotic iteration method
In this article we show that the asymptotic iteration method (AIM) allows one
to numerically find the quasinormal modes of Schwarzschild and Schwarzschild de
Sitter (SdS) black holes. An added benefit of the method is that it can also be
used to calculate the Schwarzschild anti-de Sitter (SAdS) quasinormal modes for
the case of spin zero perturbations. We also discuss an improved version of the
AIM, more suitable for numerical implementation.Comment: 10 pages, LaTeX; references added; substantially expanded versio
Split fermion quasi-normal modes
In this paper we use the conformal properties of the spinor field to show how
we can obtain the fermion quasi-normal modes for a higher dimensional
Schwarzschild black hole. These modes are of interest in so called split
fermion models, where quarks and leptons are required to exist on different
branes in order to keep the proton stable. As has been previously shown, for
brane localized fields, the larger the number of dimensions the faster the
black hole damping rate. Moreover, we also present the analytic forms of the
quasi-normal frequencies in both the large angular momentum and the large mode
number limits.Comment: 11 pages, 7 figures, version 2 added reference
Graviton emission from simply rotating Kerr-de Sitter black holes: Transverse traceless tensor graviton modes
In this article we present results for tensor graviton modes (in seven
dimensions and greater, ) for greybody factors of Kerr-dS black holes
and for Hawking radiation from simply rotating (n+4)-dimensional Kerr black
holes. Although there is some subtlety with defining the Hawking temperature of
a Kerr-dS black hole, we present some preliminary results for emissions
assuming the standard Hawking normalization and a Bousso-Hawking-like
normalization.Comment: 12 pages, 18 figure
Angular Eigenvalues of Higher-Dimensional Kerr-(A)dS Black Holes with Two Rotations
In this paper, following the work of Chen, L\"u and Pope, we present the
general metric for Kerr-(A)dS black holes with two rotations. The corresponding
Klein-Gordon equation is separated explicitly, from which we develop
perturbative expansions for the angular eigenvalues in powers of the rotation
parameters with .Comment: 10 pages, no figures. To appear in the proceedings of 2011 Shanghai
Asia-Pacific School and Workshop on Gravitatio
Bulk dominated fermion emission on a Schwarzschild background
Using the WKBJ approximation, and the Unruh method, we obtain semi-analytic
expressions for the absorption probability (in all energy regimes) for Dirac
fermions on a higher dimensional Schwarzschild background. We present an
analytic expression relating the absorption probability to the absorption
cross-section, and then use these results to plot the emission rates to third
order in the WKBJ approximation. The set-up we use is sufficiently general such
that it could also easily be applied to any spherically symmetric background in
-dimensions. Our results lead to the interesting conclusion that for
bulk fermion emission dominates brane localised emission. This is an example
contrary to the conjecture that black holes radiate mainly on the brane.Comment: 13 pages, 3 figure
Fermion excitations of a tense brane black hole
By finding the spinor eigenvalues for a single deficit angle (d-2)-sphere, we
derive the radial potential for fermions on a d-dimensional black hole
background that is embedded on a codimension two brane with conical
singularity, where the deficit angle is related to the brane tension. From this
we obtain the quasi-normal mode spectrum for bulk fermions on such a
background. As a byproduct of our method, this also gives a rigorous proof for
integer spin fields on the deficit 2-sphere.Comment: 7 pages, 1 figur
Quasi-normal modes for doubly rotating black holes
Based on the work of Chen, L\"u and Pope, we derive expressions for the
dimensional metric for Kerr-(A)dS black holes with two independent
rotation parameters and all others set equal to zero: . The Klein-Gordon equation is then explicitly separated on this
background. For this separation results in a radial equation coupled
to two generalized spheroidal angular equations. We then develop a full
numerical approach that utilizes the Asymptotic Iteration Method (AIM) to find
radial Quasi-Normal Modes (QNMs) of doubly rotating flat Myers-Perry black
holes for slow rotations. We also develop perturbative expansions for the
angular quantum numbers in powers of the rotation parameters up to second
order.Comment: RevTeX 4-1, various figure
Asymptotic iteration method for spheroidal harmonics of higher-dimensional Kerr-(A)dS black holes
In this work we calculate the angular eigenvalues of the -dimensional
{\it simply} rotating Kerr-(A)dS spheroidal harmonics using the Asymptotic
Iteration Method (AIM). We make some comparisons between this method and that
of the Continued Fraction Method (CFM) and use the latter to check our results.
We also present analytic expressions for the small rotation limit up to
with the coefficient of each power up to , where
and ( is the angular velocity, the
frequency and the cosmological constant).Comment: 7 pages, 6 tables, LaTeX; typos corrected and reference added; table
clarity improved, 2 figures and more references added (now 9 pages
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