Abstract Title

Simulations of Convective Flash Flood Events in Southern Switzerland

Faculty Mentor Name

Curtis James

Format Preference

Oral and Poster Presentation

Abstract

High-resolution Weather Research and Forecasting (WRF) model simulations were run for convective flash flood events with high peak discharges and flash flooding of the Maggia River in the Lago Maggiore region of southern Switzerland. The mesoscale mechanisms behind the observed convective training were studied to obtain insight into the atmospheric conditions that produce these events. Model verification was performed using radar-estimated rainfall totals (Panziera et al. 2015) and routine Radiosonde Observations from Milan, Italy. Mean atmospheric characteristics were analyzed using temporal averaging of the WRF output fields during the periods of heaviest precipitation over the Maggia catchment for each event as determined by the model composite reflectivity. Confluence of low-level southerly and easterly jets was observed in the cavity of the Alps surrounding the Lago Maggiore region. Furthermore, model omega and mixing ratio fields indicated significant downsloping and drying of the flow on the northern lee slope of the Apennines which led to deflection of the flow and the formation of the easterly barrier jet. The flow pattern was enhanced by a lee cyclone in the Piedmont region of northwest Italy, and the amount of the convective triggering over the region was related to the intensity of the convergence of the low-level flow. The confluence of these flow features and resultant orographic lifting of conditionally unstable air in the southerly LLJ are likely the mechanisms for the frequent convective triggering leading to intense flash floods in the Lago Maggiore region.

Invited Oral Presentation

Event Website

http://hazylibrary.erau.edu/research/undergraduate-research-institute/

Location

AC1-ATRIUM

Start Date

3-31-2017 11:00 AM

End Date

3-31-2017 3:00 PM

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Mar 31st, 11:00 AM Mar 31st, 3:00 PM

Simulations of Convective Flash Flood Events in Southern Switzerland

AC1-ATRIUM

High-resolution Weather Research and Forecasting (WRF) model simulations were run for convective flash flood events with high peak discharges and flash flooding of the Maggia River in the Lago Maggiore region of southern Switzerland. The mesoscale mechanisms behind the observed convective training were studied to obtain insight into the atmospheric conditions that produce these events. Model verification was performed using radar-estimated rainfall totals (Panziera et al. 2015) and routine Radiosonde Observations from Milan, Italy. Mean atmospheric characteristics were analyzed using temporal averaging of the WRF output fields during the periods of heaviest precipitation over the Maggia catchment for each event as determined by the model composite reflectivity. Confluence of low-level southerly and easterly jets was observed in the cavity of the Alps surrounding the Lago Maggiore region. Furthermore, model omega and mixing ratio fields indicated significant downsloping and drying of the flow on the northern lee slope of the Apennines which led to deflection of the flow and the formation of the easterly barrier jet. The flow pattern was enhanced by a lee cyclone in the Piedmont region of northwest Italy, and the amount of the convective triggering over the region was related to the intensity of the convergence of the low-level flow. The confluence of these flow features and resultant orographic lifting of conditionally unstable air in the southerly LLJ are likely the mechanisms for the frequent convective triggering leading to intense flash floods in the Lago Maggiore region.

Invited Oral Presentation

http://commons.erau.edu/pr-discovery-day/2017/posters-and-demonstrations-presentations/26