Overshooting Tops — Satellite-based Detection Methods

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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.


Category Language Difficulty Audio Duration Author
Atmosphere English Intermediate 30 min Petra Mikus

Links

Overshooting Tops presentation (PDF, 3 MB)

Downloadable Shockwave Flash files (ZIP, 6 MB)

Overshooting Tops (EUMeTrain)

Parallax Correction Tables at Convection Working Group (EUMETSAT, ESSL)

Convection Working Group (EUMETSAT, ESSL)

References

References

Bedka, K.M., 2010: Overshooting cloud top detections using MSG SEVIRI Infrared brightness temperatures and their relationship to severe weather over Europe. Atmos. Res., doi: 10.1016/j.atmosres.2010.10.001.

Bedka, K. M., Brunner, J., Dworak, R., Feltz, W., Otkin, J., Greenwald, T., 2010: Objective Satellite–Based Detection of Overshooting Tops Using Infrared Window Channel Brightness Temperature Gradients. J. Appl. Meteor.Climatol., 49, 181–202.

Brunner, J.C., Ackerman, S.A., Bachmeier, R. M., 2007: A quantitative analysis of the enhanced–V feature in relation to severe weather. Wea. Forecasting, 22, 853–872.

Doswell, C.A., 1993: Severe Convective Weather and Associated Disasters in North America. Proceedings, International Workshop on Observations/Forecasting of Mesoscale Severe Weather and Technology of Reduction of Relevant Disasters, Tokyo, Japan, 22–26 February 1993, 21–28.

Fujita,T.T., 1992: Memoirs of an effort to unlock the mystery of severe storms. WRL Research Paper 239, University of Chicago Wind Research Lab, 298 pp.

Kwon, E.H., Sohn, B.J., Schmetz, J., Watts, P., 2009: Use of ozone channel measurements for deep convective cloud height retrievals over the tropics. 16th Conference on Satellite Meteorology and Oceanography, 11–15 January, 2009, Phoenix, AZ, USA.

Lindsey, D.T., Grasso, L., 2008: An effective radius retrieval for thick ice clouds using GOES. J. Appl. Meteor. Climatol., 47, 1222–1231.

Machado, L.A.T., Lima, W.F.A., Pinto, O., Morales, C.A., 2009: Relationship between cloud-to-ground discharge and penetrative clouds: a multi-channel satellite application. Atmos. Res., 93, 304–309.

Martin, D.W., Kohrs, R.A., Mosher, F.R., Medaglia, C.M., Adamo, C., 2008: Over-ocean validation of the Global Convective Diagnostic. J. Appl. Meteor.Climatol., 47, 525–543.

Rosenfeld, D., Woodley, W.L., Lerner, A., Kelman, G., Lindsey, D.T., 2008: satellite detection of severe convective storms by their retrieved vertical profiles of cloud particle effective radius and therodynamic phase. J.Geophys. Res., 113, D04208, doi:10.1029/2007JD008600.

 
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