Search Results

You are looking at 1 - 10 of 19 items for

  • Author or Editor: R. J. Trapp x
  • Refine by Access: All Content x
Clear All Modify Search
R. J. Trapp

Abstract

Three storms intercepted during the Verification of the Origins of Rotation in Tornadoes Experiment generated a moderate-to-strong mesocyclone within the lowest several hundred meters above the ground and qualitatively appeared capable of tornadogenesis, yet did not produce a tornado. Such novel observations of what is considered“tornadogenesis failure” are documented and used to show the insufficiency of a low-level mesocyclone for tornadogenesis. Possible modes of failure are discussed.

Full access
Geoffrey R. Marion
and
Robert J. Trapp

Abstract

Although tornadoes produced by quasi-linear convective systems (QLCSs) generally are weak and short lived, they have high societal impact due to their proclivity to develop over short time scales, within the cool season, and during nighttime hours. Precisely why they are weak and short lived is not well understood, although recent work suggests that QLCS updraft width may act as a limitation to tornado intensity. Herein, idealized simulations of tornadic QLCSs are performed with variations in hodograph shape and length as well as initiation mechanism to determine the controls of tornado intensity. Generally, the addition of hodograph curvature in these experiments results in stronger, longer-lived tornadic-like vortices (TLVs). A strong correlation between low-level mesocyclone width and TLV intensity is identified (R 2 = 0.61), with a weaker correlation in the low-level updraft intensity (R 2 = 0.41). The tilt and depth of the updraft are found to have little correlation to tornado intensity. Comparing QLCS and isolated supercell updrafts within these simulations, the QLCS updrafts are less persistent, with the standard deviations of low-level vertical velocity and updraft helicity approximately 48% and 117% greater, respectively. A forcing decomposition reveals that the QLCS cold pool plays a direct role in the development of the low-level updraft, providing the benefit of additional forcing for ascent while also having potentially deleterious effects on both the low-level updraft and near-surface rotation. The negative impact of the cold pool ultimately serves to limit the persistence of rotating updraft cores within the QLCS.

Full access
M. Toth
,
R. J. Trapp
,
J. Wurman
, and
K. A. Kosiba

Abstract

In the United States, visual observations of tornadoes and/or the existence of tornado damage currently provide the sole evidence of tornadogenesis in association with a mesocyclone or other radar-detected storm-scale vortex. The severity of the tornado damage is currently the only means of estimating the intensity of tornadoes, radar detected or otherwise. The limitations of the damage-based record of tornado occurrence and intensity are well known and motivated this research. Weather Surveillance Radar-1988 Doppler (WSR-88D) measurements of the translating tornadic flow were compared with (semi-) coordinated measurements obtained near the surface with mobile radar. On the basis of a small yet fairly broad sample of tornadoes, high linear correlation was found between the vortex intensity (rotation plus translation) quantified using WSR-88D data and that quantified using Doppler on Wheels data. The possible effects of Doppler radar sampling on these results were explored through experiments with a simple vortex model. These experiments argued that the likelihood is high that a tornado would be sampled in a favorable way during at least one radar scan. Hence, the suggestion from this work is that WSR-88Ds (or similar operational radars) can potentially be used in isolation to estimate low-level tornado intensity. The proposed estimation is by way of a linear regression model, and application of this model is relevant only once a tornado is already confirmed.

Full access
Sonia Lasher-Trapp
,
Enoch Jo
,
Luke R. Allen
,
Bryan N. Engelsen
, and
Robert J. Trapp

Abstract

The current study identifies and quantifies various mechanisms of entrainment, and their diluting effects, in the developing and mature stages of a simulated supercell thunderstorm. The two stages, differentiated by the lack or presence of a rotating updraft, are shown to entrain air by different, but related mechanisms that result from the strong vertical wind shear of the environment. The greatest entrainment rates in the developing stage result from the asymmetric overturning of large eddies near cloud top on the downshear side. These rates are greater than those published in the literature for cumuli developing in environments lacking strong shear. Although the entrainment rate increases exponentially in time throughout the developing stage, successive cloud turrets help to replenish some of the lost buoyancy and condensate, allowing the nascent storm to develop further. During the mature stage, the greatest entrainment rates occur via “ribbons” of horizontal vorticity wrapping around the rotating updraft that ascend in time. The smaller width of the ribbons in comparison to the wider storm core limits their dilutive effects. Passive tracers placed in the low-level air ingested by the mature storm indicate that on average 20% of the core contains some undiluted air from below the storm base, unaffected by any entrainment mechanism.

Open access
Robert J. Trapp
,
Geoffrey R. Marion
, and
Stephen W. Nesbitt

Abstract

Strong to violent tornadoes cause a disproportionate amount of damage, in part because the width and length of a tornado damage track are correlated to tornado intensity (as now estimated through enhanced Fujita scale ratings). The tendency expressed in the observational record is that the most intense tornadoes are often the widest. Herein the authors explore the simple hypothesis that wide intense tornadoes should form more readily out of wide rotating updrafts. This hypothesis is based on an application of Kelvin’s circulation theorem, which is used to argue that the large circulation associated with a wide intense tornado is more plausibly associated with a wide mesocyclone. Because a mesocyclone is, strictly speaking, a rotating updraft, the mesocyclone width should increase with increasing updraft width. A simple mathematical model that is quantified using observations of mesocyclones supports this hypothesis, as do idealized numerical simulations of supercellular thunderstorms.

Full access
Robert J. Trapp
,
Geoffrey R. Marion
, and
Stephen W. Nesbitt
Full access
Jacob R. Carley
,
Benjamin R. J. Schwedler
,
Michael E. Baldwin
,
Robert J. Trapp
,
John Kwiatkowski
,
Jeffrey Logsdon
, and
Steven J. Weiss

Abstract

A feature-specific forecasting method for high-impact weather events that takes advantage of high-resolution numerical weather prediction models and spatial forecast verification methodology is proposed. An application of this method to the prediction of a severe convective storm event is given.

Full access
David M. Plummer
,
Jeffrey R. French
,
David C. Leon
,
Alan M. Blyth
,
Sonia Lasher-Trapp
,
Lindsay J. Bennett
,
David R. L. Dufton
,
Robert C. Jackson
, and
Ryan R. Neely

Abstract

Analyses of the radar-observed structure and derived rainfall statistics of warm-season convection developing columns of enhanced positive differential reflectivity Z DR over England’s southwest peninsula are presented here. Previous observations of Z DR columns in developing cumulonimbus clouds over England were rare. The observations presented herein suggest otherwise, at least in the southwesterly winds over the peninsula. The results are the most extensive of their kind in the United Kingdom; the data were collected using the National Centre for Atmospheric Science dual-polarization X-band radar (NXPol) during the Convective Precipitation Experiment (COPE). In contrast to recent studies of Z DR columns focused on deep clouds that developed in high-instability environments, the COPE measurements show relatively frequent Z DR columns in shallower clouds, many only 4–5 km deep. The presence of Z DR columns is used to infer that an active warm rain process has contributed to precipitation evolution in convection deep enough for liquid and ice growth to take place. Clouds with Z DR columns were identified objectively in three COPE deployments, with both discrete convection and clouds embedded in larger convective complexes developing columns. Positive Z DR values typically extended to 1–1.25 km above 0°C in the columns, with Z DR ≥ 1 dB sometimes extending nearly 4 km above 0°C. Values above 3 dB typically occurred in the lowest 500 m above 0°C, with coincident airborne measurements confirming the presence of supercooled raindrops. Statistical analyses indicated that the convection that produced Z DR columns was consistently associated with the larger derived rainfall rates when compared with the overall convective population sampled by the NXPol during COPE.

Full access
R. J. Trapp
,
E. D. Mitchell
,
G. A. Tipton
,
D. W. Effertz
,
A. I. Watson
,
D. L. Andra Jr.
, and
M. A. Magsig

Abstract

Tornadic vortex signatures (TVSs) of 52 tornadoes were identified and analyzed, then characterized as either descending or nondescending. This characterization refers to a known tendency of radar-observed tornadic vortices, namely, that of their initial detection aloft and then of their subsequent descent leading to tornadogenesis. Only 52% of the sampled TVSs descended according to this archetypal model. The remaining 48% were detected first near the ground and grew upward or appeared nearly simultaneously over a several kilometer depth; these represent primary modes of tornado development that have been explained theoretically. The descending–nondescending TVSs were stratified according to attributes of the tornado and TVS. Significantly, tornadoes within quasi-linear convective systems tended to be associated with nondescending TVSs, identification of which provided a mean tornado lead time of 5 min.

Two case studies are presented for illustrative purposes. On 1 July 1997 in southern Minnesota, nondescending TVSs and associated tornadogenesis were revealed in the leading edge of a squall line, with a squall line–supercell merger, and later during that day, with the cyclonic bookend vortex of a bow echo. On 22 June 1995 in southern Colorado, a low-topped supercell storm produced a tornado that was associated with a descending TVS.

Full access
G. K. Grice
,
R. J. Trapp
,
S. F. Corfidi
,
R. Davies-Jones
,
C. C. Buonanno
,
J. P. Craven
,
K. K. Droegemeier
,
C. Duchon
,
J. V. Houghton
,
R. A. Prentice
,
G. Romine
,
K. Schlachter
, and
K. K. Wagner
Full access