Impact of Massive Supercell Observed in Space

- the First Clear Evidence that Severe Meteorological Events Affect the Ionosphere -

November 1, 2013

Abstract

The National Institute of Information and Communications Technology (NICT, President: Dr. Masao Sakauchi) has observed ionospheric variations caused by a severe tropospheric event: a supercell, which generated an EF-5 tornado in Moore, Oklahoma, USA, in May 2013. The high-resolution and wide-coverage ionospheric maps revealed two types of remarkable ionospheric variations, concentric waves and short-period oscillations. This observational result provides the first clear evidence of a severe meteorological event causing atmospheric waves propagating upward in the upper atmosphere and reaching the ionosphere. Moreover, the result implies that the ionospheric observation can provide information on meteorological events in the future.

Background

The ionosphere, the upper atmosphere around 300 km altitude, has been considered to be affected by lower atmospheric variations as well as solar activity and magnetospheric storms. However, the relationship between the ionosphere and severe meteorological events has not been fully understood yet since the ionospheric observations did not have enough spatial resolution and coverage. NICT has developed high-resolution ionospheric total electron content (TEC) maps using dense GPS receiver networks. The TEC maps make it possible to monitor ionospheric variations in detail.

Observations

Concentric waves observed in the high-resolution TEC map over North America

Concentric wave structures were observed in the TEC maps one to two hours after the massive tornado hit Moore. They had been observed traveling throughout North America for more than seven hours. Short-period TEC oscillations were also observed in the vicinity of Moore. A comparison between the TEC maps and infrared cloud images from the GOES satellite indicates that the concentric waves and short-period oscillations were caused by supercell-induced atmospheric gravity waves and acoustic resonances, respectively. This observational result provides the first clear evidence of a severe meteorological event causing atmospheric waves propagating upward in the upper atmosphere and reaching the ionosphere.

Future Prospects

This study is important in identifying the relationship between the ionosphere and the atmosphere. Moreover, the result implies that the ionospheric observation can provide information on meteorological events in the future. The details of this study will be published in “Geophysical Research Letters”
(http://onlinelibrary.wiley.com/doi/10.1002/2013GL057963/abstract).

Appendix

Fig.1 Schematic picture of atmospheric waves and the ionospheric variations after the 2013 Moore tornado

Ionospheric variations around 300 km altitude were observed using two-frequency GPS signals transmitted from satellites at about 20,000 km altitude and recorded by ground GPS receivers (more than 2,600 stations distributed in North America). It is considered that the atmospheric waves were excited by a powerful supercell which generated the massive tornado at Moore. These atmospheric waves propagated up to 300 km altitude, and generated the concentric structures in the ionosphere.

Fig.2 Concentric waves observed in TEC perturbation maps

TEC represents total number of electrons in a unit area column. The TEC data are detrended values derived by subtracting 20-minute running average of the data. TEC perturbation maps of two, three, and four hours after the supercell generations are shown here. The city of Moore is represented by a red star. The circles represent the concentric wavefronts detected by the TEC map. The center of the concentric waves is designated by a cross mark.

Fig.3 Supercells captured in Infrared images by the GOES-13 satellite

The evolution of the supercell, which produced the massive tornado outbreak, was captured in a infrared image by the NOAA GOES satellite. The brightness of the image represents cloud-top height. The red and green arrows indicate the locations of the developing supercells in Oklahoma and Texas, respectively.