Hail Occurence: relationship to intraseasonal oscillation

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Sunday, 2 February 2014
Hall C3 (The Georgia World Congress Center )
B.S. Barrett, U.S. Naval Academy, Annapolis, MD; and B. Henley

The Madden-Julian Oscillation describes the eastward propagation of planetary-scale atmospheric waves from the Indian Ocean to the Central Pacific and beyond. Although the MJO itself is equatorially trapped and thus its primary influences are experienced in the tropics, it does impact the mid-latitudes through modification of Rossby Waves. Understanding the mechanisms by which the MJO affects the mid-latitude wave train may lead to more predictability of extreme weather, including severe convective storms and hail. For example, a direct correlation exists between an active MJO cycle and extreme precipitation, whereby an active MJO results in heavy rainfall. Substantial research has demonstrated the connection between the MJO and other U.S. weather events including surface temperature, lightening, and tornadoes.

However, much is still unknown about whether the MJO cycle modulates extreme events such as hail. The purpose of this study is to better understand the relationship between the MJO and hail, in order to increase predictability. Hail embryos begin as super-cooled water droplets in cumulonimbus clouds. Strong updrafts force the droplets higher into the atmosphere in which they freeze. Downdrafts allow the hail embryos to collect more super-cooled water droplets and the process continues. This local-scale process is controlled by the larger-scale atmosphere, suggesting possible modulation by the MJO. This study will allow one to determine the extent to which hail formation is influenced by MJO, the regions in the United States where hail is most likely to occur during specific MJO phases, and during which time periods. Extending the predictability of severe events into the one to two week window will allow citizens to prepare and thus act to minimize the effects of storms.