REU Home | Participants | Mentors | Projects | Lectures & Workshops | Field Trips & Tours | Schedules | Photos
student: Diana Blahyj, State University of New York -
Brockport
mentor: Dave Imy, Storm Prediction Center
abstract
Fast moving bow echoes typically produce a significant
amount of wind damage, especially along the bowing portion of the line. On 12
March 2001, a line of severe thunderstorms with embedded bow echoes and mesolows
moved rapidly through the southeastern United States. This bow echo produced
wind damage along the bowing portion of the line early in the day, however,
a majority of the severe weather events occurred with mesolows/mesocyclones
located within the line after 1500 UTC. This paper focuses on the evolution
of the mesolows and severe weather that occurred on this particular day.
student: David Bolen - University of Northern Colorado
mentors: Bob Johns and John Hart, Storm Prediction Center
abstract
This preliminary study examines the occurrence of strong and violent tornadoes
to determine the relationship between convective initiation, tornado occurrence,
and boundary location. Tornadoes were gathered from events occurring during
the warm (Jun.-Aug.) and cool (Jan.-Mar.) season portions of 1991, as well as
a spring transition season major outbreak on 26 April. The majority of strong
and violent tornado episodes occurred on or near preexisting surface boundaries.
Isolated events (1-2 tornadoes) had the highest association with preexisting
surface boundaries, while outbreak events (> 10 tornadoes) varied widely been
episodes. This was especially true when comparing the outbreak of 26 April with
the other outbreaks of the period.
Boundaries also served as favored spots for convective initiation, but the convection
did not necessarily stay on the initiation boundaries until the tornado occurred.
In fact, in 70% of the cases, the convection moved off of the boundary in which
it initiated, and tornado(es) occurred on different boundaries or in different
sectors. In the majority of these cases, the tornado(es) occurred on large-scale
outflow boundaries generated by the convection or convective cluster. Some implications
of future work are also discussed.
Student: Sara Bruening, Univerisity of Wisconsin at Milwaukee
Mentors: Mike Kay, Storm Prediction Center and Harold Brooks, National Severe
Storms Laboratory
abstract
The climatology of tornadoes is considered using only the most fundamental
aspects of the historical tornado record: the daily number of tornadoes and
the annual number of tornadoes for the period 1955-1999. This study attempts
to define what is a normal tornado year given the fact that the raw number of
tornadoes has nearly doubled since 1955. Two methods are employed to determine
a normal year: the first is to remove any secular trends from the observed data
while the second uses a rudimentary numerical model to simulate 10,000 years
of daily tornado activity. Once a normal year has been defined, climatological
aspects of any year such as departures from normal can be computed. Results
suggest that data through the end of April are required in order to make judgments
about the outcome of the tornado year.
Student: Kristen Delack, Pennsylvania State University
Mentors: Dave Andra, Mike Foster, Dan Miller, National Weather Service Forecast
Office
abstract
During the early morning hours of 11 April 2001 a mini outbreak of tornadoes
occurred across central and southern Oklahoma. The storms that affected the
area were not as strong or as organized as traditional tornadic supercell thunderstorms,
nor were they low-topped like tornadic mini-supercell thunderstorms. Most of
the tornadoes produced that morning, however, were rated F1 or F2 on the Fujita
scale and were responsible for one fatality, five injuries, and over $3.1 million
in damage. This case and two similar cases were examined to determine radar
characteristics of these atypical tornadic storms. Analysis of Doppler radar-retrieved
data, such as mesocyclone rotational velocity, mesocyclone diameter, height
of maximum rotational velocity, and height of storm top was performed. Results
indicated that these storms do not fit the conceptual model for classic, LP,
HP, or mini-supercells. Rather, they reflected characteristics of both mini-
and traditional supercells. The strength and diameter of the mesocyclones were
similar to those of mini-supercells, however, the storm top heights were substantially
higher than those of mini-supercells. The height of maximum rotational velocity
was much lower than that of both mini- and traditional supercells. Although
this is a limited data set, the conclusion can be made that these storms represent
another region of the tornadic storm spectrum that is not well documented.
Student: Nettie Lake, Lyndon State College
Mentor: Don MacGorman, National Severe Storms Laboratory
abstract
Several studies have indicated that the dominant polarity of a thunderstorm
may predict the severity of the thunderstorm. This study examines the differences
in the location of thunderstorms dominated by positive cloud-to-ground lightning
(initially positive storms) and of thunderstorms dominated by negative cloud-to-ground
flashes (negative storms) relative to a surface equivalent potential temperature
(theta-e) ridge. Previous studies suggest that a surface theta-e maximum separates
initially positive storms on the upstream side of the ridge from negative storms
on the downstream side. This study found that most initially positive storms
form on the side of increasing theta-e relative to storm motion. Initially positive
storms will usually cross the ridge axis and become dominated by negative cloud-to
ground flashes. Other initially positive storms move adjacent to the ridge axis
and remain positive. Some initially positive storms do not form near a theta-e
ridge. Negative storms were thought to form downstream of a theta-e maximum,
but this study found otherwise, as only 17% of negative storms examined formed
downstream of the maximum. Nearly equal amounts of negative storms cross the
axis, move adjacent to it, or do neither. Very few negative storms reversed
dominant polarity, and if they did, it was during the final stages of the storms'
duration.
Student: Adam Lopes, Pennsylvania State University
Mentor: Kelvin Droegemeier, Center for Analysis and Prediction of Storms
abstract
The establishment of a statistical climatology of storm cell characteristics
has long been a goal of the atmospheric research community. Yet, the large amounts
of data necessary for such a project, coupled with an incomplete radar Level
II data archive, made this sort of endeavor impossible. In 1998, however, the
Center for Analysis and Prediction of Storms at the University of Oklahoma began
the Collaborative Radar Acquisition Field Test (or Project CRAFT) as an effort
to equip WSR-88D radars with the capability to compress and transmit Level II
data over the Internet in real time. For 2 years the CRAFT radars have been
continuously transmitting data, assembling a Level II data archive that is nearly
100% complete. The success of Project CRAFT has presented the enabling technology
to begin a statistical climatology of storm cell characteristics. Therefore,
this pilot study was done in order to identify several methods through which
a statistical climatology can be constructed. Storm events were selectively
chosen for this study. After the Level II radar data from Dallas/Ft. Worth radar
(KFWS) was collected for each event and run through the Storm Cell Identification
and Tracking (SCIT) Algorithm, the data was analyzed several different ways.
Analysis techniques include developing frequency distributions of cell characteristics,
examining relationships among the cell characteristics, and plotting the cell
characteristics spatially using GIS software. Spatial plots were then related
to the locations of Dallas/Ft. Worth Airport and major airways into and out
of this airport. These analysis techniques proved to be beneficial, as several
conclusions were reached that may, upon the compilation of years of radar data,
lead to the development of a credible statistical climatology of storm cell
characteristics. Furthermore, the results presented from this small data set
show great promise for the potential utility of such a climatology for air traffic
considerations at large airports.
Student: Mario Lopez, University of Texas Pan American
Mentor: Ken Howard, National Severe Storm Laboratory
abstract
Biological hotspots are small geographical areas that contain much of Earth's
biodiversity. Humans significantly threaten these areas and the species that
reside in them with destruction. Moreover, because these biological hotspots
occur in such small areas of the Earth, it is necessary to study whether a relationship
exists between climates and the biological hotspots. Climate change could affect
biological hotspots if such a relationship exists. This paper seeks to demonstrate
that a direct relationship exists between climate regimes and biological hotspots.
Student: Alison Marr, Murray State
Mentor: Kim Elmore, National Severe Storms Laboratory
abstract
To date, ensemble cloud modeling has mainly been used as a research tool.
An ensemble cloud model that uses the Kessler precipitation parameterization
has been used to generate forecasts of storm lifetimes. This project examines
how an ice parameterization scheme changes the ensemble storm lifetimes. For
each of the six cases, the storm lifetimes from the model without ice and model
with ice are compared to the observed storm lifetimes to determine if adding
ice statistically improves the forecast storm lifetimes. Quantitatively, only
one case shows improvement when ice is added to the model. However, qualitatively,
a majority of the cases improve when ice is included.
Student: Cathryn Meyer, Boston College
Mentor: Harold Brooks, National Severe Storms Laboratory
abstract
A statistically based model of the hazard associated with significant tornadoes
(F2 or greater on the Fujita scale) based on the reports recorded from 1921-1995
in the United States is developed. The model consists of four components. The
first is a probability that at least one tornado will occur at a grid point
(grid spacing is approximately 80 km on a side) on any day of the year at any
location in the United States. The second component is a model of the number
of tornadoes reported per day in a single grid box, given that at least one
tornado occurs. Third, the intensity of each tornado on the Fujita scale is
determined, based on the historical distribution of intensity. Finally, the
path length and width of the tornado are modeled using Weibull distributions
for each value of the F-scale. The model has been run for 30,000 years, with
almost 4,000,000 tornadoes produced in order to develop reliable statistics.
The peak areal coverage of tornadoes (at a grid point in southern Oklahoma)
is about 3% of a grid box per century, implying a return period for strong and
violent tornadoes at any point in that grid box of about 3000 years. The model
also shows the dangers of using a short period of record to estimate tornado
hazards. Differences in 15-year periods of 50% in mean tornado occurrence are
observed in the model, even without changing any of the parameters. This result
has significance for the assessment of risk using the 'raw' observations and
for detection of changes in the climatology of tornado occurrence.
Student; Jason Tomlison, Valparaiso University
Mentor: Dave Rust, National Severe Storms Laboratory
abstract