Analysis of Tornado-Induced Tree Fall Using Aerial Photography from the Joplin, Missouri, and Tuscaloosa–Birmingham, Alabama, Tornadoes of 2011

In this study, aerial imagery of tornado damage is used to digitize the falling direction of trees (i.e., tree fall) along the 22 May 2011 Joplin, Missouri, and 27 April 2011 Tuscaloosa–Birmingham, Alabama, tornado tracks. Normalized mean patterns of observed tree fall from each tornado’s peak-intensity period are subjectively compared with results from analytical vortex simulations of idealized tornado-induced tree fall to characterize mean properties of the near-surface flow as depicted by the model. A computationally efficient method of simulating tree fall is applied that uses a Gumbel distribution of critical tree-falling wind speeds on the basis of the enhanced Fujita scale. Results from these simulations suggest that both tornadoes had strong radial near-surface winds. A few distinct tree-fall patterns are identified at various locations along the Tuscaloosa–Birmingham tornado track. Concentrated bands of intense tree fall, collocated with and aligned parallel to the axis of underlying valley channels, extend well beyond the primary damage path. These damage patterns are hypothesized to be the result of flow acceleration caused by channeling within valleys. Another distinct pattern of tree fall, likely not linked to the underlying topography, may have been associated with a rear-flank downdraft (RFD) internal surge during the tornado’s intensification stage. Here, the wind field was strong enough to produce tornado-strength damage well beyond the visible funnel cloud. This made it difficult to distinguish between tornado- and RFD-related damage and thus illustrates an ambiguity in ascertaining tornado-damage-path width in some locations

Heat, moisture, and momentum budgets of a midlatitude squall line with a trailing stratiform region

October 1989.Also issued as author's thesis (M.S.) -- Colorado State University, 1989.Includes bibliographical references.Rawinsonde data from the 1985 O-K PRE-STORM project are used to calculate the heat, moisture and momentum budgets during the late mature through decaying stages of a large squall line system that occurred on 10-11 June. Rawinsondes are composited to decrease station spacing and allow better resolution of mesoscale features within t he system. Low-level radar data and surface accumulated rainfall reports are used to partition the convective system into convective line and stratiform regions, and to check the accuracy of the heat and moisture budgets. Despite the compositing approach, the spacing of the sounding data is inadequate to fully resolve motions in the convective line. The resolution is marginally adequate, however, for motions in the stratiform region. This squall line had a pronounced rear-inflow jet that advanced toward the front of the system with time, and strong front-to-rear flow at higher levels. Convergence was strong in mid-levels within the stratiform region where the opposing jets met. Divergence at the top of the system weakened markedly as the system decayed. Upward vertical motion also weakened, and the vertical axes of strongest convective line ascent and descent within the stratiform region became increasingly sloped over time. Heating rates within the overall convective system peaked around 400 mb near the convective line region, and decreased in intensity from over 13°C h - 1 to less than 5°C h - 1 between 0300 and 0730 UTC. Cooling occurred in the stratiform region and was most intense just behind the back edge of the radar echo around 550 mb, just above the melting level. Peak cooling rates increased from over 3°C h- 1 to 6°C h- 1 between 0300 and 0600 UTC, and then decreased to 4°C h - 1 at 0730 UTC. Drying rates peaked also in the convective line region, but at lower levels than the heating rates. Moistening due to evaporation was typically strongest around 700 mb in the stratiform region. Vertical integrations of both budgets produced rainfall rates generally close to the observed ones for averages over the entire system. However, precipitation in the leading convective line was underestimated by 40% , due in large part to inadequate sounding data resolution. In the stratiform region the diagnosed precipitation rates underestimated the observed by as much as 2 or 3 _mm h-1 as the system decayed. Radar reflectivity data showed that the rearward transport · of hydrometeors could add as much as 2 - 4 mm h- 1 to the diagnosed stratiform rates. The transport, in addition to liquid water storage, could account for the underestimations in the diagnosed rates. The fact that the underestimate in the stratiform region did not occur at 0300 UTC suggests that vertical motion in the convective line was aliased into the stratiform region significantly at this earlier time. Less aliasing may have occurred later as the leading line weakened and the separation between it and the stratiform region increased. In general, the location of predicted rainfall and the temporal trend of the heating and moistening rates matched observations well, establishing the credibility of the budget studies. A strong mesolow existed at mid-levels within the stratiform region of the system, and the momentum budget showed pressure gradient accelerations were generally front-to-rear. Coriolis accelerations and internal turbulent stresses generally opposed the pressure gradient, and the resulting observed accelerations became weak, with increasing rear-to-front acceleration at high levels as the system weakened. The pressure gradient increased the vertical shear of the component of the wind normal to the line, but as the system decayed, the turbulent stresses began to oppose the increase in shear.Supported by the National Science Foundation under grant no. ATM-8711649, and a National Science Foundation graduate fellowship

An example of a virtual reality learning environment

Using photographic, computer graphical and experimental data, a pilot model of a tornadic supercell thunderstorm was created in a virtual environment at Iowa State University. One goal of the project was to give students the virtual experience of being in the field, experiencing the dramatic features of typical tornadic supercells, and stimulating them to explore and ask questions in this learning environment. Initial feedback from the prototype version was favorable

Observational and Modelling Study of a Major Downburst Event in Liguria : the 14 October 2016 Case

Downbursts are very disruptive weather events that can produce large amounts of damage. The most studied downbursts are those occurring in the United States and continental Europe, but they can happen globally. This work is an observational and modelling analysis of a major downburst event that occurred on 14 October 2016 over eastern Liguria (Italy). This downburst affected an area 30 km long and 10 km wide, producing observed wind gusts of 40 m/s with major impacts to railways, trees, and houses, with more than 2.5 million euros of damage. First, the general environment influencing this downburst is identified and analyzed, then the event is reproduced with a small multi-physics high-resolution ensemble using the Weather Research and Forecasting (WRF)-advanced research WRF (ARW) model, with 1 km horizontal grid spacing. The event was poorly predicted beforehand, and the difficulty in forecasting this event is confirmed by the fact that so few ensemble members suggested the occurrence of damaging winds over eastern Liguria. However, one of the eight members performed well and its output helped to reveal the primary mechanisms for the downburst, suggesting that high-resolution ensembles using mixed physics may be a useful tool for improving the prediction of similar extreme events in the Mediterranean region in the future