Seasonally and Diurnally Varying Cold Front Effects along the Minnesotan North Shore of Lake Superior

Cold fronts are typically associated with cooling, drying and a strengthening wind that shifts to have a northerly component. Cold front effects at a particular point, however, are dependent upon pre-existing air mass characteristics. Here, we examine 634 passages of synoptic-scale cold fronts in northeastern Minnesota from 2010 to 2018. While these fronts are associated with the expected effects in some areas, they are often associated with warming and enhanced drying in the region directly influenced by an air mass from Lake Superior (coastal sites). Coastal sites experience warming during more than half of cold frontal passages, in contrast to proximate inland sites out of the influence of the lake. This warming, combined with a removal of the moist lake air mass, often leads to a sharp post-front decrease in relative humidity. These relatively unusual local effects indicate a need to carefully consider characteristics of the lake air mass and likely changes during cold frontal passage when forecasting regional temperature and fire weather conditions

Radar quantification, temporal analysis and influence of atmospheric conditions on a roost of American Robins (\u3ci\u3eTurdus migratorius\u3c/i\u3e) in Oklahoma

Radar observations present a way to monitor large, mobile populations across long temporal scales, and are especially valuable when individual scatterers are challenging to count visually. The focus of this study is a large and relatively homogeneous wintertime roost of American Robins (Turdus migratorius) in central Oklahoma. Radar observations are used to estimate the roost population through winter 2010–2011, and the population time series is related to weather variables and radar beam propagation. Radar-estimated roost population gradually increased to an estimated peak of 1.5–2 million individuals from November 2010 to January 2011, and then decreased in a more stepwise manner through the spring until roost dispersal in early March. Weather conditions did not definitively explain these population decreases leading toward roost dispersal. Birds from the roost were often observed to travel \u3e50 km away during the daytime. About 25–30% of the variability in the radar-derived roost population estimate could be explained by atmospheric variables. This work provides an example of how radar methods may be used to estimate populations and monitor their temporal trends, which may be valuable to conservation efforts by facilitating estimates of population change through time

Tornado Knowledge and Perceptions as an Influence on Safety Actions Taken: Preliminary Results

During fall 2012, 613 UNL students in introductory‐level science courses were surveyed. Questions asked included home location and years lived in Nebraska, source from which participants learned about tornadoes and tornado safety, general responses to tornado warnings, specific responses to the most recent tornado warning experienced, and a variety of questions designed to test knowledge of tornadoes and appropriate tornado safety actions. Preliminary results will be presented for a subset of this data, with a focus on: 1) Geographic differences in participant knowledge of tornadoes and tornado safety, 2) Relationships between source of tornado‐related knowledge, source of tornado warnings, and responses to tornado warnings, and 3) How perceptions of tornadoes may influence actions participants report to take when under a tornado warning

Bioscatter transport by tropical cyclones: insights from 10 years in the Atlantic basin

Tropical cyclones (TCs) can transport birds and insects near their center of circulation. In this study, we examined the maximum altitude, area and density of the radar-derived bioscatter signature across a set of 42 TC centers of circulation sampled from 2011 to 2020. All TC events contained at least one time when a bioscatter signature was present. More intense hurricanes with closed eyes typically had taller and denser bioscatter signatures, and sometimes larger areas dominated by bioscatter. This indicated a larger number of organisms within the circulation of more intense hurricanes, supporting the speculation that those storms were most likely to trap birds that do not want to risk flying through their eyewall thunderstorms. Larger and denser bioscatter signatures, indicating a larger number of birds, tend to occur when fall migration brings a large bird population to the Gulf and East Coasts where most storms were sampled. TC formation location was not related to bioscatter characteristics, but storms sampled in the Gulf of Mexico and Florida tended to have larger and denser bioscatter signatures

Mesocyclone and Microphysical Evolution in Simulated Supercell Storms with Varying Wind and Moisture Profiles

As a high-impact convective mode, supercell thunderstorms have frequently been studied observationally and numerically. Two areas of study have focused on understanding mesocyclone evolution given a varying environmental wind profile, and learning about microphysical distributions within supercells. In the research presented here, simulations are run over a broad parameter space of wind profiles, and with a smaller number of profiles representative of environmental drying at mid and upper levels. Mesocyclone evolution is compared across the parameter space of wind profiles, and between simulations with liquid and ice microphysics. Effects of the wind profile and moisture variations are explored on microphysical distributions. Subsequently, possible effects of these microphysical variations on supercell evolution are considered.When using detailed ice microphysics with this particular choice of thermodynamic profile, mesocyclone evolution is shown to be more frequently non-occluding cyclic with no steady non-cycling storms. Storms with detailed ice microphysics are shown to have warmer cold pools, and to more rapidly concentrate vertical vorticity at low levels. The single feature found to most influence low-level mesocyclone structure was an RFD westerly surge proceeding from the echo appendage and moving eastward into the updraft region. This westerly surge often produced a new or strengthened updraft pulse, often caused a cycling process to ensue, and was the southern limit of the primary near-surface vertical vorticity maximum. Quantity and spatial distribution of warm rain and hail from frozen drops may affect downdraft temperature and thus strength of this RFD surge. Associations are explored between maximum warm rain mixing ratio and variables related to RFD intensity and near-surface vertical vorticity. Mid- and upper-level drying reduced content of small ice particles and warm rain, while increasing content of hail from frozen drops. Bursts of warm rain and hail from frozen drops were often associated with increasing near-surface vertical vorticity, apparently related to an intensified RFD westerly surge

Novice Explanations Of Hurricane Formation Offer Insights Into Scientific Literacy And The Development Of Expert-Like Conceptions

The ability to explain scientific phenomena is a key feature of scientific literacy, and engaging students’ prior knowledge, especially their alternate conceptions, is an effective strategy for enhancing scientific literacy and developing expertise.  The gap in knowledge about the alternate conceptions that novices have about many of Earth’s complex phenomena (National Research Council, 2012), however, makes this type of engagement in geoscience courses challenging.  This study helps to fill this gap by identifying and describing how novices to geoscience explain a complex scientific phenomenon, hurricane formation.  Using a pragmatism methodology, 326 students in introductory-level geoscience courses at two public universities in the United States of America, in Georgia (n=168) and Nebraska (n=158), were surveyed.  The questionnaire was designed to target and collect novices’ explanations of a single complex Earth phenomenon – hurricane formation.  Constant comparative analyses of textual content and diagrams revealed a variety of alternate conceptions.  The data suggess that novices seldom invoke scientific first principles, which students matriculating through the education system are expected to learn before college, in their explanations.  Two theoretical models synthesize the alternate conceptions and illustrate pathways of conceptual change along which students might move from more novice-like to more expert-like ways of scientific thinking.  Our findings provide a basis for the development of instructional activities that aid students in developing more expert-like conceptions of hurricane formation and other complex Earth phenomena

Impact of Past Experiences with Tornadoes on Future Decisions in Nebraska

The National Weather Service (NWS) advises the public to go to an interior room on the lowest level of their houses when a tornado warning is issued for their area. As the NWS Central Region Service Assessment of the Joplin, Missouri Tornado published in July 2011 reveals, however, this is often not the first action taken after learning that there is danger of being hit by a tornado. Rather, people need to seek confirmation from more than one source before following the recommended action. The goal of this research project is to determine how the number of sources and what sources residents use vary with respect to characteristics such as the intensity of their past experiences. A total of 20 residents from two small Nebraskan towns were interviewed. The town of Pilger was hit by an EF4 tornado on June 16, 2014. St. Helena was hit by a weak tornado in the late 1960s. Residents were first asked to share how they would respond to a given situation. Next, they were questioned about how they responded during past experiences with tornadoes. Analysis of these interviews is ongoing, and results will be presented at the conference

Measurement and characterization of infrasound from a tornado producing storm

A hail-producing supercell on 11 May 2017 produced a small tornado near Perkins, Oklahoma (35.97, –97.04) at 2013 UTC. Two infrasound microphones with a 59-m separation and a regional Doppler radar station were located 18.7 and 70 km from the tornado, respectively. Elevated infrasound levels were observed starting 7min before the verified tornado. Infrasound data below ~5Hz was contaminated with wind noise, but in the 5–50 Hz band the infrasound was independent of wind speed with a bearing angle that was consistent with the movement of the storm core that produced the tornado. During the tornado, a 75 dB peak formed at ~8.3 Hz, which was 18 dB above pre-tornado levels. This fundamental frequency had overtones (18, 29, 36, and 44 Hz) that were linearly related to mode number. Analysis of a larger period of time associated with two infrasound bursts (the tornado occurred during the first event) shows that the spectral peaks from the tornado were present from 4min before to 40 min after tornadogenesis. This suggests that the same geophysical process(es) was active during this entire window

Land-Cover Change and the ‘‘Dust Bowl’’ Drought in the U.S. Great Plains

The North American Dust Bowl drought during the 1930s had devastating environmental and societal impacts. Comprehending the causes of the drought has been an ongoing effort in order to better predict similar droughts and mitigate their impacts. Among the potential causes of the drought are sea surface temperature (SST) anomalies in the tropical Pacific Ocean and strengthened local sinking motion as a feedback to degradation of the land surface condition leading up to and during the drought. Limitations on these causes are the lack of a strong tropical SST anomaly during the drought and lack of local anomaly in moisture supply to undercut the precipitation in the U.S. Great Plains. This study uses high-resolution modeling experiments and quantifies an effect of the particular Great Plains land cover in the 1930s that weakens the southerly moisture flux to the region. This effect lowers the average precipitation, making the Great Plains more susceptible to drought. When drought occurs, the land-cover effect enhances its intensity and prolongs its duration. Results also show that this land-cover effect is comparable in magnitude to the effect of the 1930s large-scale circulation anomaly. Finally, analysis of the relationship of these two effects suggests that while lowering the precipitation must have contributed to the Dust Bowl drought via the 1930s land-cover effect, the initiation of and recovery from that drought would likely result from large-scale circulation changes, either of chaotic origin or resulting from combinations of weak SST anomalies and other forcing