PNNL

The Science

Most warm season storms in the U.S. are associated with deep convection and exhibit distinct patterns in their rainfall intensity, duration, and size, with differing regional distributions. However, the lack of a reliable long-term observational dataset that includes important characteristics of deep convection has hampered understanding of its regional variations. Scientists have developed a new high-spatiotemporal resolution (4 km, hourly) observational dataset of mesoscale convective systems (MCSs) and isolated deep convection (IDC) in the U.S. east of the Rocky Mountains from 2004–2017. The product shows that both MCS and IDC are essential contributors to regional precipitation but possess significantly different spatiotemporal characteristics.

The Impact

This paper details a novel data product based on tracking convective systems at different spatiotemporal scales over a long period of time. The data can be used to investigate the environments associated with either MCS or IDC as well as examine the impacts of the convective systems on surface hydrology, atmospheric chemistry, severe weather hazards, and other aspects of the energy, water, and biogeochemical cycles. The data also provides an important benchmark for evaluating and improving the representation of different convective processes in weather and climate models.

Summary

The researchers updated the Flexible Object Tracker algorithm to simultaneously track both MCSs and IDC. Using the computational resources from the National Energy Research Scientific Computing Center, they applied the updated algorithm to an hourly satellite dataset of brightness temperature, radar reflectivity, and precipitation. The algorithm then produced a synthesized high-resolution observational data product showing MCSs and IDC over the U.S. east of the Rocky Mountains from 2004–2017. The results show that MCSs are much larger and longer-lasting than IDC, but that IDC with a mean convective intensity comparable to that of the MCSs occurs about 100 times more frequently. Hence, both MCSs and IDC are essential contributors to both mean and extreme precipitation east of the Rocky Mountains but exhibit significantly different spatiotemporal characteristics. IDC precipitation is concentrated in the summer in the Southeast with a peak in the late afternoon, while MCS precipitation is significant in all seasons, especially spring and summer in the Great Plains. The spatial distribution of MCS precipitation amounts varies by season, while diurnally, MCS precipitation generally peaks during nighttime except in the Southeast.

PNNL Contact

L. Ruby Leung, Pacific Northwest National Laboratory, Ruby.Leung@pnnl.gov 

Funding

This research was supported by the U.S. Department of Energy Office of Science Biological and Environmental Research as part of the Regional and Global Modeling and Analysis (RGMA) program area through the collaborative, multi-program Integrated Coastal Modeling project. The research was also partly supported by the Water Cycle and Climate Extremes Modeling Scientific Focus Area funded by RGMA. The research used computational resources from the National Energy Research Scientific Computing Center, a DOE user facility supported by the Office of Science under Contract DE-AC02-05CH11231.