An overshooting convective cloud top (OT) is a dome-like protrusion above a cumulonimbus anvil, often penetrating into the lower stratosphere. It is a manifestation of a very strong updraft in the convective cloud.
Published: 9 June 2011
An OT forms when a thunderstorm's updraft, due to momentum from rapid ascent and strength of lifting, protrudes its equilibrium level (the point where the surrounding air is about the same temperature or even warmer) near the tropopause region and penetrates into the lower stratosphere. This can occur within any cumulonimbus cloud when instability is high.
OTs can be most easily identified in the high-resolution visible channel imagery as the lumpy textured appearance, however only during the daytime. In the 10.8 µm infra-red window (IRW) channel, available during both day and night, a small cluster of very cold brightness temperatures can indicate that an OT is present.
Satellite-based methods for the detection of convective clouds and the heights of their tops are usually based on IRW measurements. Research by the authors has shown that OTs can be detected from the satellite data using the brightness temperature difference (BTD) of the water vapour and the IR channel (6.2–10.8 µ m), BTD of the ozone and IR channel (9.7–10.8 µ m) or BTD of carbon dioxide and IR channel (13.4–10.8 µ m). A combination of the 6.2-10.8 µ m and 9.7-10.8 µ m BTDs can also be used. All these methods include thresholds for both IR brightness.
According to some investigations, deep convective storms with OTs often produce hazardous weather conditions such as heavy rainfall, damaging winds, large hail, cloud-to-ground lightning and tornadoes. These events can cause considerable property damages, influence everyday activities and even endanger the human lives.
Locations and times of the appearance of the detected OTs are compared with the occurrence of the wind gusts, temperature drop, humidity increase and precipitation measured by the automatic stations.
At the end of this lecture you will be able to:
- understand the dynamics of the Overshooting Tops;
- identify the Overshooting Tops in satellite images;
- demonstrate the relationship between overshooting cloud top and the severe weather conditions;
- describe methods of Overshooting Tops detection using satellite imagery.
Pre-requisites: Basic knowledge of VIS and IR imagery of thunderstorm clouds.
|Atmosphere||English||Intermediate||✓||30 min||Petra Mikus|
Overshooting Tops presentation (PDF, 3 MB)
Downloadable Shockwave Flash files (ZIP, 6 MB)
Parallax Correction Tables at Convection Working Group (EUMETSAT, ESSL)