Electromagnetic Noise Studies of Severe Convective Storms in Iowa: The 1970 Storm Season

Electromagnetic noise from six convective storms in Iowa has been studied at a variety of frequencies from 0.67 to 144 MHz, with the majority of the data being recorded at 53 MHz. The quasi-static atmospheric electric field was also studied. Twelve tornadoes, numerous funnel clouds and several hailstorms occurred during these storms. Eleven of the tornadoes appear to correlate with some type of enhancement of the recorded electromagnetic pulse rate. A spectacular peak in pulse rate during Storm No. 5 is attributed to a brief but destructive tornado at 38 km; the event is discussed in detail. One tornado at long range, the longest lived of the season, showed no correlation and is thought to represent a minority class of tornadoes which exhibit little electromagnetic noise generation. Good time correlation is also achieved between data events and several hailstorms and funnel clouds. Except for the closest events (\u3c20 km), the region above 1 MHZ appears to be a better indicator of tornadic activity than that portion of the radio spectrum below 1 MHz. The data also reveal a number of pulse-rate peaks which could not be correlated with known severe weather events. Four and possibly five types of radio noise observed from severe storms are described, along with some initial suggestions about the possible mechanisms involved. The lack of understanding of the basic physics involved is indicated and the need for more observational data is emphasized

Investigating knowledge building dialogues in networked communities of practice. A collaborative learning endeavor across cultures

We have analyzed data from two online courses, designed to promote collaborative online learning, and in the contexts of two different cultures. Ongoing assessment (self, group, instructor) that actively engages students within the course (as opposed to instructor assessment at the end) is a central feature for achieving collaborative knowledge building in online dialog. Careful articulation and deployment of assessment criteria is a design feature that promotes meta-awareness, which, in turn, together with student-centeredness and operationalization of student experiences in the design of the curriculum, enhances student participation, motivation and ownership in the dialog. From eight years of experience with online dialog and two quite different implementations we offer a set of design principles, having a sound theoretical basis, that enhance the quality and quantity of online knowledge building. Our analysis suggests that the characteristics of the discussion threads emerging under these design criteria give evidence of true collaborative learning.We have analyzed data from two online courses, designed to promote collaborative online learning, and in the contexts of two different cultures. Ongoing assessment (self, group, instructor) that actively engages students within the course (as opposed to instructor assessment at the end) is a central feature for achieving collaborative knowledge building in online dialog. Careful articulation and deployment of assessment criteria is a design feature that promotes meta-awareness, which, in turn, together with student-centeredness and operationalization of student experiences in the design of the curriculum, enhances student participation, motivation and ownership in the dialog. From eight years of experience with online dialog and two quite different implementations we offer a set of design principles, having a sound theoretical basis, that enhance the quality and quantity of online knowledge building. Our analysis suggests that the characteristics of the discussion threads emerging under these design criteria give evidence of true collaborative learning

Climate change projections of the North American Regional Climate Change Assessment Program (NARCCAP)

We investigate major results of the NARCCAP multiple regional climate model (RCM) experiments driven by multiple global climate models (GCMs) regarding climate change for seasonal temperature and precipitation over North America. We focus on two major questions: How do the RCM simulated climate changes differ from those of the parent GCMs and thus affect our perception of climate change over North America, and how important are the relative contributions of RCMs and GCMs to the uncertainty (variance explained) for different seasons and variables? The RCMs tend to produce stronger climate changes for precipitation: larger increases in the northern part of the domain in winter and greater decreases across a swath of the central part in summer, compared to the four GCMs driving the regional models as well as to the full set of CMIP3 GCM results. We pose some possible process-level mechanisms for the difference in intensity of change, particularly for summer. Detailed process-level studies will be necessary to establish mechanisms and credibility of these results. The GCMs explain more variance for winter temperature and the RCMs for summer temperature. The same is true for precipitation patterns. Thus, we recommend that future RCM-GCM experiments over this region include a balanced number of GCMs and RCMs

Changes in extreme, cold-season synoptic precipitation events under global warming

We analyze regional climate model (RCM) simulations of daily, spatially distributed extreme precipitation events, using co-operative network observations and output from 10-year RCM simulations of present and future-scenario climates. We examine an Upper Mississippi River Basin region during October–March for daily amounts that exceed the 99.95th percentile and that occur simultaneously at several observation sites or model grid points. For the observations and each simulation, nearly all such extreme regional events occur when a slow moving, cut-off-low system develops over the Rockies and Great Plains and steadily pumps moisture into the Upper Mississippi region from the Gulf of Mexico. The threshold for the extreme events increases in the future scenario by an amount similar to the increase in saturation specific humidity. The results suggest robust circulation behavior for such extremes in the face of climate change