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During the summer of 1998, the REU student participants were involved in some very interesting research. Some of them examined severe weather phenomena such as: flash floods, hail, lightning, tornadoes, shortwave troughs, and supercell thunderstoms. Others attacked problems dealing with regional climatologies, meteorological instrumentation, and weather warning systems. At the conclusion of the program, the students wrote their research papers and presented their findings orally to other members of the Oklahoma Weather Center scientific community.
The students had access to research facilities at the National Severe Storms Laboratory, the University of Oklahoma College of Geosciences, National Weather Service Forecast Office, the Storm Prediction Center, the Center for Analysis and Prediction of Storms, the Oklahoma Climatological Survey, the Cooperative Institute for Mesoscale Meteorological Studies, and the University of Oklahoma library system. Below are the students' research abstracts from this past summer.
SHORTWAVE TROUGHS AND VIOLENT TORNADO OUTBREAKS
Student: Alicia Cacciola
State University of New York at Albany
Mentor: Robert Johns-Storm Prediction Center
ABSTRACT: It has been noticed that violent tornado outbreaks are often accompanied by rapidly moving shortwave troughs or wind maxima at mid-levels of the atmosphere. The goal of this project was see if there is an actual relationship between violent tornado outbreaks and rapidly moving jet streaks. In cases of tornado outbreaks, wind maxima or shortwave trough axes were tracked as they moved across the country. Their speed and magnitude were compared to the speed and magnitude of wind maxima associated with wind and/or hail severe weather outbreaks.
RELATIONSHIP BETWEEN EASTERLY WAVES AND SURGES OVER THE GULF OF CALIFORNIA DURING THE MEXICAN MONSOON
Student: Ryan Dean Fuller
Northland College, Ashland Wisc.
Mentor: David Stensrud-National Severe Storms Laboratory
ABSTRACT: Steady increasing concerns have prompted need for improved weather forecasting over the Southwest United States in recent years. With factors including increasing population and economic demands, monsoonal climates affect more people than ever before. In just three months, the main convective weather system of the region, the Mexican Monsoon, produces approximately 30-50% of all rainfall over the southwestern United States and as much as 70% over Mexico. In past years, forecasters have found difficulties predicting surge events that lead to the formations of heavy rains and severe weather outbreaks caused by the monsoonal conditions. The use of Mesoscale models (e.g.Eta) display the lowest accuracy over this region and too few surface observation mount to the difficulties.
In past studies, it was believed that the Gulf of Mexico and the Caribbean were the sources of moisture leading to the monsoon, see Jurwitz (1953). In the1970's Hales (1972), concluded that the Gulf of California was the likely source, but could not explain the mechanisms involved. The Stensrud et al. (1997) study showed that there is a relationship between easterly waves leading to surges found propagating north from the Gulf of California on at least one event. This most current study examined a 13 year period to see if that relationship is sound. Relationships among three features are examined over southwest Arizona. Those include surge passages over Yuma, 850 hPa meridional wind speed, and 200 hPa meridional wind speed.. With high accuracy, results conclude that approximately 2 days after easterly waves occur drastic changes occur signaling surge events. Without easterly waves, significant surge events did not occur with high frequency.
ON HAIL FORECASTING SCHEMES AND FUTURE DIRECTIONS
Student: Christopher Rozoff
University of Wisconsin at Milwaukee
Mentor: Harold Brooks-National Severe Storms Laboratory
Mentor: Jeff Craven-Storm Prediction Center
ABSTRACT: Operationally, no objective standards are evaluated for the prediction of hail size. Various hail size prediction schemes have been developed and are observed in this paper. In particular, a parameter defined as the product of convective available potential energy (CAPE) and bulk Richardson number shear divided by the product of the wet bulb zero height level and average wet bulb temperature below the wet bulb zero height level is tested. Forecast skill testing shows this parameter and other thermodynamic variables to be poor indicators of hail size. A scheme using a one-dimensional cloud model and forecast skew-t log-p diagrams, appears to be the most favorable route for future development, based upon this paper's results. Results from the data lead to questions about the observations of maximum hail size.
OASIS98 OKLAHOMA ATMOSPHERIC SURFACE-LAYER INSTRUMENTATION SYSTEM
Student: Christopher McAloon
Mentor: Scott Richardson-Cooperative Institute for Mesoscale Meteorological Studies
ABSTRACT: The OASIS (Oklahoma Atmospheric Surface-layer Instrumentation System) Project, supported by the National Science Foundation, is enhancing the existing Oklahoma Mesonet over the next two years by adding a system of surface flux stations. These flux stations will directly measure the net radiation and ground heat flux and indirectly estimate the sensible heat flux; latent heat flux will be calculated as a residual from the energy balance equation. In addition, selected stations will directly measure all four components of the energy budget including sensible and latent heat fluxes.
The OASIS98 Field Project, conducted from 27 June to 8 August 1998, was designed to assess the accuracy of surface fluxes measured using OASIS instrumentation. For this project, the National Center for Atmospheric Research's (NCAR) Atmosphere-Surface Turbulent Exchange Research (ASTER) Facility was used. The ASTER Facility measures surface fluxes by eddy-correlation and measures atmospheric profiles of temperature, moisture, and wind speed and direction. In this paper, the ASTER-measured surface fluxes, which serve as a reference, are compared to those made using OASIS instrumentation. This comparison provides an estimate of the uncertainty associated with OASIS measurements.
DEVELOPMENT OF THE CWA DATABASE AND TESTING
Student: Gregg Gallina
Mentor: J.T. Johnson-National Severe Storms Laboratory
ABSTRACT: The National Severe Storms Laboratory (NSSL) has developed the Warning Decision Support System (WDSS), to provide warning guidance information to meteorologists for their use during warning situations. Putting the information in a tabular format that lists storms in order of severity helps alert the forecaster to the most significant storms at a given time. The current WDSS design only processes data from a single WSR-88D. A newer algorithm, the County Warning Area (CWA) algorithm, will combine algorithm products from multiple radar into a single integrated CWA Algorithm Guidance Table. The table will provide information about which radar is the "best", "2nd best", and possibly "3rd best", for each phenomenon. A rule-base must be created and tested, to verify the algorithm's logic and practicality.
COEVOLUTION OF LIGHTNING STRIKES AND STORM STRUCTURE
Student: Christina Hannon
Mentor: Don MacGorman-National Severe Storms Laboratory
ABSTRACT: A preliminary analysis of cloud-to-ground lightning and storm structure in the tornadic supercells of 8 June 1998 in central Oklahoma. The third storm from the GOES-8 satellite image in central Oklahoma was a right mover, produced large hail and two tornadoes. The Maud tornado occurred from 1811 CST to 1815 CST and the Wewoka/Yeager tornado occurred from 1835 CST to 1915 CST. The polarity of the cloud-to-ground lightning changed from positive to negative and the hail size decreased at the time of the tornadoes.
ARE POTENTIAL VORTICITY ANOMALIES ASSOCIATED WITH FLASH FLOODS
Student: Steven Decker
Mentor: David Schultz-National Severe Storms Laboratory
ABSTRACT: A suite of numerical weather prediction models, along with observations, was used to attempt to determine whether midtropospheric potential vorticity anomalies are, in fact, associated with flash-flood events, as has been suggested. Two cases (27 June 1995 in Madison County, VA and 16 June 1996 in Ames, IA) were examined in detail. Three other floods were given a cursory analysis. The results are strongly suggestive that, in many cases, potential vorticity anomalies can be associated with these events, although limited model resolution in some cases inhibited a definitive answer
SIZE, SPACING, AND PREDICTABILITY OF DEEP CONVECTIVE STORMS
Student: Russell Teabeault
Mentor: Kelvin Droegemeier-Center for Analysis an Prediction of Storms
ABSTRACT: A three dimensional numerical model s used to conduct a preliminary study of the factors responsible for determining the size and spacing of deep convective storms. Two sets of simulations are conducted in a 80X80 km domain with periodic lateral boundaries. The first uses random potential temperature perturbations to initiate convection so that the scale and spacing of the storms may be determined "naturally". The second uses a checkerboard pattern of various sized potential temperature perturbations to force storms at particular scales and spacings. For the two sets of experiments, simulations were run with both a calm and strongly sheared wind profile' the thermodynamic profile was the same in all cases.
When random forcing is used, supercell storms form in a the
strong shear environment and tend to be larger in size than the
single-cells in the counterpart no-wind run. When perturbations
of a particular scale are used to trigger convection, the resulting
storms seem to have a "memory" of that scale which
tends to last longer as the size of the initiating disturbances
is increased. Nonetheless, the supercell storms in strong shear
tend to be larger in these experiments as well. It is apparent
that the environment, particularly the vertical shear, plays
a major and perhaps, the key role in determining storm size and
spacing.
CLIMATOLOGY OF WARM SEASON MORNING PRECIPITATION SYSTEMS
AND THEIR ENVIRONMENTS
Student: Jill Derby
North Carolina State University
Mentor: Carl Hane-National Severe Storms Laboratory
Mentor: David Andra-National Weather Service Forecast Office
ABSTRACT: A minimum of thunderstorm activity has been observed during the late morning hours in the Great Plains region. This minimum is the result of dissipation of nocturnal activity slightly earlier in the day and development of new activity in the early afternoon. This time period is of particular interest to forecasters because of uncertainty in whether systems will survive or dissipate. A climatological study has been done for 8 summer months during morning hours within the Norman, OK and Dodge City, KS forecast areas. A total of 181 precipitation systems that occurred on 127 days were identified based upon archived hourly precipiation data. The track of each system was determined and statistics on direction of motion compiled. Comparisons between system motion and direction of 500 mb flow were made. A limited assessment of the importance of surface fronts and troughs was carried out. The evolution of each system was noted for both the data set as a whole and individual flow regions, and the tendency for system dissipation during this period of the day was confirmed.
EFFECTS OF SHORTWAVE TROUGHS AND TORNADO FORMATION
Student: Jamie Casto
Mentor: Charles Doswell-National Severe Storms Laboratory
ABSTRACT: Anecdotal forecaster experience has long suggested an association between shortwave troughs and tornadoes. In this study, this association is explored by examining 500 mb charts for all the shortwave troughs meeting certain criteria and considering their association with significant tornado (F-2 and greater) occurrences during May of 1957 and May of 1987. It was found that only 15% of shortwave troughs produce a significant tornado during their existence, but that most significant tornadoes (~25%) are associated either with a significant shortwave trough or with a synoptic-scale cut-off cyclone.
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