# Recent Advances and Challenges in the Seismo-Electromagnetic Study: A Brief Review
## 3 Seismo-Electromagnetic Phenomena in the Lower Atmosphere  
The seismo-electromagnetic phenomena in the lower atmosphere include atmospheric electric field perturbations, earthquake lights [72; 73], thermal anomalies [74; 75; 76], and so on. The anomaly of atmospheric electric fields, possibly associated with earthquakes, is an interesting seismo-electromagnetic phenomenon in the lower atmosphere. There are some independent observations of earthquake-related anomalies of the atmospheric electric field after the Ms 7.8 Tangshan earthquake in China. To verify the reliability of the atmospheric electric precursors, one research group of the Institute of Geophysics has made continuous observations and carried out some studies on this topic since 1976. They obtained empirical relationships between the anomalies of the atmospheric electric field and earthquakes, and applied them to some earthquake prediction tests [77]. Recently, anomalous negative signals observed by ground-based atmospheric electric field instruments under fair weather conditions were considered a novel earthquake prediction approach [78]. One of the best-documented observations of earthquake lights is from Japanese earthquakes, where bright lights at the ground level were photographed from 20 to 200 m in diameter with a duration from 10 s to 2 min, restricted to mountain summits in a quartz-diorite faulted rock [73]. Luminous phenomena were reported, starting at approximately nine months before the 6 April 2009 earthquake and continuing until approximately five months after the shock [72]. A statistical study of lightning activity and M \(\geq\) 5.0 earthquakes in the Taiwan region showed lightning activities tending to appear around the forthcoming epicenter and being enhanced a few days before shallow land earthquakes [79]. Possible explanations about earthquake lights include ultrashort-period air oscillations and generation of potential differences by the piezoelectric effect [80].  
The thermal anomalies include atmospheric temperature, brightness temperature, surface latent heat flux (SLHF), outgoing longwave radiation, thermal infrared spectral range (TIR), etc. For example, the preseismic anomalies of SLHF were observed by [PERSON] et al. [81], and they reported surface temperature anomalies before two major earthquakes [82]. [PERSON] et al. [76; 83] reported thermal radiation anomalies associated with some major earthquakes, showing that infrared signals were observed near the epicenter areas and stayed from several hours to a few days. [PERSON] et al. [84] adopted the broadly used robust satellite technique data analysis methodology to identify the significant sequence of thermal anomalies acquired by multi-functional transport satellite (MTSAT) over Japan, confirming a noncausal correlation between anomalies and earthquakes. [PERSON] et al. [74] proposed a statistically well-founded definition of TIR anomalies for satellite TIR surveys. A probability gain of up to 3.7 was achieved as far as only significant sequences of TIR anomalies preceding earthquakes were considered. In practice, the remote sensing of thermal infrared anomalies can be affected by cloud coverage [85], and sometimes it is hard to discriminate thermal contributions that are possibly connected to seismic activity in cloudy conditions [86].