Operational uses for an objective overshooting top detection algorithm

Developed by researchers at the Cooperative Institute for Meteorological Satellite Studies, the infrared-only objective overshooting top (OT) algorithm relies only on infrared channel brightness temperature gradient (or texture), tropopause temperature from numerical weather prediction models, and pre-defined OT size and brightness temperature. Therefore, it is possible to detect OTs regardless of time of day. This algorithm has been shown to operate well with any high spatial resolution (≤ 4 km) geostationary or polar-orbiting ~11 micron infrared window channel image. This algorithm can be used to investigate the relationships between OT activity and: 1) the tropical cyclone intensification process, 2) aircraft observations of turbulence, 3) the El Niņo Southern Oscillation (ENSO). This presentation will highlight recent analyses and case studies of OT activity in tropical cyclones, aviation turbulence encounters, and throughout the ENSO.

As seen during Hurricane Wilma, a spike in the number of OTs occurred coincidently with and increase in maximum wind speed. Further verification of increased overshooting top quantities indicating tropical cyclone intensification can be seen along the hurricane track, with a majority of the OTs occurring to the left of the hurricane track. This OT analysis is also extended to other tropical cyclones, including Katrina and Rita.

OTs are also an inference of airplane reported turbulence, since within 25 km of an OT Bedka et al . (J .Appl. Meteor. And Climatol., 2009) determined there is a 25% frequency of light or greater turbulence and a 5% frequency of moderate or greater turbulence. A case study of Pinnacle flight 2871, which made an emergency landing in Louisville, Kentucky, on August 4, 2004, after encountering turbulence, indicates that the flight tracked within 25 km of an overshooting top.

Finally, overshooting tops have a climatological impact, as water vapor is transferred from the troposphere to the stratosphere. The difference between the number of overshooting tops with respect to the El Niņo Southern Oscillation is thus explored by comparing the number occurring during an El Niņo phase and a La Niņa phase. As expected, more overshooting tops occurring during El Niņo when compared with La Niņa over the equatorial tropical Pacific Ocean. Regions of greater overshooting top occurrence during La Niņa include the subtropical Pacific as well as the Eastern Pacific.