Research Activity 3 Updates

July 2020

Hello everyone! My name is Ryan Bunker and I am a second year Master’s student working on the PRES2iP team. I am originally from Mesa, Arizona, but I have been in Oklahoma since Spring 2015. I graduated from the University of Oklahoma with my B.S. in Meteorology in 2018. 

My research uses a database of observed subseasonal-to-seasonal (S2S) extreme precipitation events and radar observations to identify the leading source of precipitation and how it varies based on event type. For this work, S2S precipitation events are defined as two-week precipitation accumulations that exceed the 95th percentile accumulation for a given location and time period. This timescale was developed from the work of Gregory Jennrich, a Master’s student who previously worked on this project. 

In order to classify events, we use a radar algorithm (called the ‘Z-R relationship’) to group precipitation into different types. For example, “convective” precipitation results from the rapid upward motion that we experience in thunderstorms; “stratiform” precipitation results from gentle upward motion that we see with layered (somewhat boring) clouds. Precipitation events usually have both convective and stratiform clouds, resulting in different intensities and durations of precipitation throughout the event that can contribute it becoming extreme or not. As we continue to accumulate S2S events, we will test different relationships between radar reflectivity and the type of precipitation to determine which relationships are best by region and what the characteristics of these extreme events are. Figures 1 and 2 are examples of two different radar relationship combinations that we have tested. By visualizing the data this way, it helps us determine what the dominant source of precipitation is for each region of the United States, as we believe it will vary based on geographic location.

Figure 1: Example of the fractions of convection (left) and stratiform (right) precipitation from an S2S precipitation case in the southern Plains. 
Figure 2: Example of the fractions of tropical convection (left) and cool stratiform (right) precipitation from an S2S precipitation case in the southern Plains.