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

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

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

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

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

Polarimetric Radar Observations of Biological Scatterers in Hurricanes Irene (2011) and Sandy (2012)

Biological scatterers, consisting of birds and insects, may become trapped near the circulation center of tropical cyclones, particularly if a well-developed eyewall is present. These scatterers may be observed using weather radar, where they may appear to the radar operator as areas of light precipitation. Polarimetric radar characteristics of these scatterers, informed by additional observations of known bioscatter, include a combination of very high differential reflectivity (3–7.9 dB) and very low copolar correlation coefficient (0.3–0.8). Polarimetric radar observations of bioscatter are presented for Hurricane Irene (2011) and Hurricane Sandy (2012). In these storms, the bioscatter signature first appeared at the 0.58 elevation angle at a distance of 100– 120km from the radar. The signature appeared on successively higher tilts as the circulation center neared the radar, and its areal coverage in constant altitude plan position indicator (CAPPI) slices was primarily governed by the distribution of convection in the eye and by the timing of landfall. The highest altitude at which the signature appears may represent the inversion level within certain tropical cyclone eyes. For Hurricane Irene, inland observations of oceanic bird species support biological transport. Knowledge of the bioscatter signature has value to meteorologists monitoring tropical cyclones within the range of a polarimetric radar, possible value for estimating inversion height changes within the eyes of well-structured tropical cyclones, and value to biologists who wish to estimate the magnitude of biological transport in tropical cyclones

Disdrometer, Polarimetric Radar, and Condensation Nuclei Observations of Supercell and Multicell Storms on 11 June 2018 in Eastern Nebraska

Disdrometer and condensation nuclei (CN) data are compared with operational polarimetric radar data for one multicell and one supercell storm in eastern Nebraska on 11 June 2018. The radar was located ~14.3 km from the instrumentation location and provided excellent observation time series with new low-level samples every 1–2 min. Reflectivity derived by the disdrometer and radar compared well, especially in regions with high number concentration of drops and reflectivity \u3c45 dBZ. Differential reflectivity also compared well between the datasets, though it was most similar in the supercell storm. Rain rate calculated by the disdrometer closely matched values estimated by the radar when reflectivity and differential reflectivity were used to produce the estimate. Concentration of CN generally followed precipitation intensity for the leading convective cell, with evidence for higher particle concentration on the edges of the convective cell associated with outflow. The distribution of CN in the supercell was more complex and generally did not follow precipitation intensity

METR 200: Weather and Climate—A Peer Review of Teaching Project Benchmark Portfolio

This benchmark portfolio is meant to be an assessment of how well the objectives of METR 200 (Weather and Climate) are being attained by students in several classifications of academic major. Students from a wide range of backgrounds enroll in this course as a general science elective, and for many, it will be the only science course taken in college. Thus, it is important that course material be sufficiently accessible for all students, while providing meaningful information which will be applicable by students of all backgrounds once they leave the course. In this portfolio, an analysis will be presented showing how well each of the four course objectives are being attained by students in each classification of academic major. Arising from this analysis, changes will be proposed for future sections of METR 200 which should allow the course to more fully reach its objectives among a broader sample of enrolled students