J. N. Thomas

On the onset of ionospheric precursors 40 min before strong earthquakes

Heki (2011) and Heki and Enomoto (2013) claimed that anomalous, yet similar, increases of ionospheric total electron content (TEC) started ~40 min prior to the 2011 Tohoku-Oki, as well as before other Mw > 8 earthquakes. The authors concluded that the reported TEC anomalies were likely related to the pending earthquakes, suggesting also that TEC monitoring may be useful for future earthquake prediction. Here we carefully examine the findings of Heki (2011) and Heki and Enomoto (2013) by performing new analyses of the same TEC data. Our interpretation is that the 40 min onset of the ionospheric precursors is an artifact induced by the definition of the reference line adopted in analyzing TEC variations. We also discuss this repeatability in the tectonic and geodynamic context of the earthquakes. By performing a Superimposed Epoch Analysis of TEC data, we show that, however, the TEC increase reported by Heki (2011) was not particularly anomalous. We conclude that the TEC precursors reported by Heki (2011) and Heki and Enomoto (2013) are not useful for developing short-term earthquake prediction capabilities.

Strong electric fields from positive lightning strokes in the stratosphere

[1] A balloon payload launched in Brazil has measured vector electric fields from lightning at least an order of magnitude larger than previously reported above 30 km in the stratosphere. During the flight hundreds of lightning events were recorded, including several positive cloud to ground lightning strokes. A two stroke flash, with small (15 kA peak current) and moderate (53 kA) positive strokes at a horizontal range of 34 km, produced field changes over 140 V/m at 34 km altitude. On-board optical lightning detection, recorded with GPS timing, coupled with ground based lightning location gives high time resolution for study of the electric field transient propagation. These measurements imply that lightning electric fields in the mesosphere over large thunderstorms may be much larger than previously measured. Citation: Holzworth, R. H., M. P. McCarthy, J. N. Thomas, J. Chin, T. M. Chinowsky, M. J. Taylor, and O. Pinto Jr. (2005), Strong electric fields from positive lightning strokes in the stratosphere, Geophys. Res. Lett., 32, L04809, doi:10.1029/2004GL021554.

Comment on “Temporal and spatial precursors in ionospheric total electron content of the 16 October 1999 Mw 7.1 Hector Mine earthquake” by Su et al. (2013)

We review the recent paper by Su et al. (2013). Using Global Position System and Global Ionospheric Maps data, Su et al. claimed to have found ionospheric precursors a few days before the 16 October 1999 Hector Mine, California, earthquake. They proposed that this type of analysis of ionospheric data may be useful for locating forthcoming large earthquakes. In this Comment, we reexamine these data and show that ionospheric anomalies reported by Su et al. were not precursors to the Hector Mine earthquake. Therefore, their proposed analysis is not useful in the context of earthquake prediction.

A Very Active Sprite-Producing Storm Observed Over Argentina

During the night of 22–23 February 2006, more than 400 middle-atmospheric optical discharges were observed above one large thunderstorm system over northeastern Argentina. These transient luminous events (TLEs) were imaged during the Southern Brazil Sprite Campaign, the first campaign to focus on TLEs over southern Brazil, northeastern Argentina, and Uruguay. All of the TLEs were imaged from the Brazilian Southern Space Observatory (SSO) near Santa Maria, which is nearly in the center of the southernmost Brazilian state of Rio Grande do Sul. Although the fields of view of the imaging cameras were too narrow to view the entire storm, the more than 400 confirmed TLEs imaged indicate that this storm ranks as the third most active TLE producer ever reported. Hence, storms in this region of South America might be some of the leading TLE generators on Earth.

Temporal‐spatial modeling of electron density enhancement due to successive lightning strokes

[1] We report results on the temporal-spatial modeling of electron density enhancement due to successive lightning strokes. Stroke rates based on World-Wide Lightning Location Network measurements are used as input to an axisymmetric Finite Difference Time Domain model that describes the effect of lightning electromagnetic pulses (EMP) on the ionosphere. Each successive EMP pulse interacts with a modified background ionosphere due to the previous pulses, resulting in a nonlinear electron density perturbation over time that eventually reaches a limiting value. The qualitative ionospheric response to successive EMPs is presented in 2-D, axisymmetric space. Results from this study show that the nonlinear electron density perturbations due to successive lightning strokes must be taken into account and varies with altitude. The limiting maximum electron density is reached earlier in time for higher altitudes, and the most significant effect occurs at 88 km. The limiting modeled electron density profile in the 83-91 km altitude range does not depend on the initial electron density.

A new high-voltage electric field instrument for studying sprites

The high-voltage (HV) electric field detector is a new high-voltage, high-impedance, double Langmuir probe instrument designed for stratospheric electric field measurements. In the Sprite Balloon Campaign 2002-2003, this HV instrument was used to measure electric fields between 100 and 200 V/m associated with lightning discharges, which is nearly an order of magnitude higher than previously reported above 30 km in altitude. This increased range is made possible by the availability of new low-leakage HV operational amplifiers. This is a critical instrument, since a large quasi-DC electric field associated with positive cloud-to-ground lightning is a primary component of most sprite generation mechanisms. The difficulty that exists when making electric field measurements in the high-resistance environment of the stratosphere is presented, and how this difficulty is remedied is described. The HV detector is compared to another electric field instrument, the low-voltage detector, used simultaneously on the Sprite Balloon Campaign to verify the accuracy of the HV probes. Finally, a large field perturbation (E/sub z//spl ap/-101 V/m and E/sub x//spl ap/79 V/m) measured by the HV detector during Flight 1, correlated with nearby +15-kA and +53-kA cloud-to-ground strokes, is presented.

Are there new findings in the search for ULF magnetic precursors to earthquakes

Moore (1964) in a letter published in Nature reported disturbances in geomagnetic field data prior to the 27 March 1964 Alaska earthquake. After the publication of this report, many papers have shown magnetic changes preceding earthquakes. However, a causal relationship between preearthquake magnetic changes and impending earthquakes has never been demonstrated. As a consequence, after 50 years, magnetic disturbances in the geomagnetic field are still candidate precursory phenomena. Some researchers consider the investigation of ultra low frequency (ULF: 0.001–10 Hz) magnetic data the correct approach for identifying precursory signatures of earthquakes. Other researchers, instead, have recently reviewed many published ULF magnetic changes that preceded earthquakes and have shown that these are not actual precursors. The recent studies by Currie and Waters (2014) and Han et al. (2014) aim to provide relevant new findings in the search for ULF magnetic precursory signals. However, in order to contribute to science, alleged precursors must be shown to be valid and reproducible by objective testing. Here we will briefly discuss the state of the art in the search for ULF magnetic precursors, paying special attention to the recent findings of Currie and Waters (2014) and Han et al. (2014). We do not see in these two reports significant evidence that may support the observation of precursory signatures of earthquakes in ULF magnetic records.

On the reliability of the Spatial Scintillation Index to detect earthquake precursors in the ionosphere

The scientific literature includes many reports of ionospheric phenomena that are retrospectively identified prior to seismic events. These disturbances of the Earths ionosphere are considered to be possible precursors of the impending earthquakes. However, a causal relationship between ionospheric phenomena and earthquakes has never been definitively demonstrated, and attempts at identifying precursory effects in the ionosphere have been called into question by several studies. Among the candidate indicators of ionospheric precursors there is the Spatial Scintillation Index (SSI) proposed by Pulinets et al. (2007). The usefulness of this index in the search for precursory effects of earthquakes has been criticized by Thomas et al. (2012) and Masci (2013). In a recent report, Pulinets and Davidenko (2014) attempt to briefly respond to the remarks of these researchers. Here we cast doubt that Pulinets and Davidenko (2014) have shown that SSI is a reliable indicator of precursory effects of earthquakes in the ionosphere.

A statistical study of global ionospheric map total electron content changes prior to occurrences of M ≥ 6.0 earthquakes during 2000-2014

There are many reports on the occurrence of anomalous changes in the ionosphere prior to large earthquakes. However, whether or not these changes are reliable precursors that could be useful for earthquake prediction is controversial within the scientific community. To test a possible statistical relationship between ionospheric disturbances and earthquakes, we compare changes in the total electron content (TEC) of the ionosphere with occurrences of M ≥ 6.0 earthquakes globally for 2000 - 2014. We use TEC data from the global ionosphere map (GIM) and an earthquake list declustered for aftershocks. For each earthquake, we look for anomalous changes in GIM-TEC within 2.5° latitude and 5.0° longitude of the earthquake location (the spatial resolution of GIM-TEC). Our analysis has not found any statistically significant changes in GIM-TEC prior to earthquakes. Thus, we have found no evidence that would suggest that monitoring changes in GIM-TEC might be useful for predicting earthquakes.

Evidence of underground electric current generation during the 2009 L’Aquila earthquake: Real or instrumental?

We investigate magnetic effects in correspondence of the Mw6.1 L’Aquila earthquake. Magnetic and seismic records are analyzed. Rapid and distinct changes and an offset can be seen in magnetic field components after the main shock. We show that these effects result from electromagnetic induction due to the movement of the sensors through the Earth’s magnetic field and from a permanent displacement of the sensors from their original position caused by the passing seismic waves. A transient signal in total field data from an overhauser magnetometer apparently occurs in correspondence with the earthquake. Our analysis shows that the transient was not observed by other sensors that were operating in close proximity to the overhauser. Thus, the transient signal in the total magnetic field data, and the offset in the magnetic field components, cannot be associated with a hypothetical underground electric current generated by the earthquake, as suggested by Nenovski (2015).