Extreme solar events such as CMEs (coronal mass ejections) and ICMEs (interplanetary CMEs) offer valuable information about the physical processes involved in coupling the Sun-Earth system through shocks, magnetic reconnection, wave-particle interaction, ring current intensification, geomagnetic storms, electric field intensification, and thermospheric and ionospheric storms. Seismic events including earthquakes and volcanoes provide the opportunity to understand upward coupling of the atmosphere-ionosphere system through possible magnetic/electric fields generated in the lithosphere and atmospheric waves generated in the atmospheric boundary layer during the events. In addition to scientific interest, the studies of the Sun-Earth system responses are of public interest for their effects on satellite systems and astronauts, communication and navigation, power grids and climate, and life and resources. The findings may lead to earthquake precursor and severe space weather prediction. This special section of JGR Space Physics contains a collection of papers studying the Sun-Earth system response to extreme solar and seismic events. The majority of the papers are based on the presentations in a session on this topic organized at the joint AOGS-AGU (WPGM) general assembly held in Singapore during 13–17 August 2012. The collection also contains a few papers from outside the assembly but fall within the theme of the special section. A theoretical study of Alfvén waves by Shukla [2013] provides an alternative mechanism for transferring energy from the surface of the Sun to the corona. By using a two-fluid model, together with Ampère's law, Shukla derives the wave equation for 3-D modified-kinetic Alfvén waves (m-KAWs) in a magnetoplasma. It is shown that the 3-D m-KAWs in magnetized plasma can propagate in the form of Alfvénic tornadoes characterized by plasma density whirls (or rapidly rotating magnetic flux ropes), which can channel electromagnetic wave energy and heat fluxes from the surface of the Sun into the corona through the Alfvénic tornadoes. Yue et al. [2013] study the interference of solar radio wave emissions (or solar radio bursts) that fallow solar flares with satellite signals, for example, Global Navigation Satellite System radio occultation signals from multiple satellites (COSMIC, CHAMP, GRACE, SAC-C, Metop-A, and TerraSAR-X). Thejappa et al. [2013] describe the STEREO observations of one of the most intense magnetic field aligned Langmuir wave packets ever detected in a type III radio burst. Using Dst data during 1963–2012 and OMNI data base data during 1976–2000, Yermolaev et al. [2013] present the occurrence rate of geomagnetic storms due to ICMEs, corotating interaction regions, and sheaths. Extrapolation of the results shows that a magnetic storm as large as the Carrington storm of 1859 (Dst = –1760 nT) is observed with frequency not higher than one event in ~500 years. The prompt penetration of electric field (PPEF) from the high- to low-latitude ionosphere is known to occur during geomagnetic storms. However, due to the nonavailability of direct measurements of the electric field, the difference (ΔH) between the magnitudes of the horizontal (H) component of the geomagnetic field at magnetic equatorial and off equatorial locations has usually been used to get information about PPEF during daytime when ionospheric conductivity is high. Wei et al. [2013] used the ΔH method to infer the PPEF at night when ionospheric conductivity is weak. The cross polar cap potential (CPCP), which is considered as an instantaneous monitor of the rate at which magnetic flux couples the solar wind-magnetosphere-ionosphere system, is known to saturate under extreme solar wind conditions. Gao et al. [2013] compare the performance of two models that have been used to explain the saturation of the CPCP. Balan et al. [2013] describe the recent developments in the understanding of positive and negative ionospheric storms at low and middle latitudes. Based on the neutral tendency of physical systems to occupy a minimum energy state, which is most stable, they illustrate the relative effects of electric field and neutral wind in producing positive ionospheric storms. Liu et al. [2013a] for the first time used a bias-corrected accelerated bootstrap method and a z test to detect positive and negative ionospheric storm signatures in the GPS-total electron content data measured near the equatorial ionization anomaly crest in Taiwan during 1994–2003. The possibility of using the ionosphere as a precursor of earthquake is explored in several papers. Li and Parrot [2013] used the global ion density data from the low-Earth orbiting satellite DEMETER at an altitude of 700 km for more than 6 years to automatically search for ionospheric anomalies. The anomalies are then studied using a software to identify if they correspond to earthquakes within 1500 km of the anomaly. Píša et al. [2013] use the VLF electromagnetic wave data measured by the DEMETER satellite to check whether the presence of statistically significant changes of natural wave intensity (due to lightning) relate to preseismic activity; the study is conducted for about 8400 earthquakes occurred in 6.5 years. Liu et al. [2013b] use a statistical approach to study the potential relation between ELF-whistlers/emissions (< 100 Hz) and precursor of earthquake for the 20 earthquakes of magnitude ≥ 5.0 occurred in Taiwan in a year in 2003–2004. The CHAMP satellite has been providing high-resolution thermospheric mass density data for a decade. By applying the multivariable least squares fitting method to the data, Liu et al. [2013c] construct an empirical model of the thermospheric mass density. The model describes the density variation with latitude, longitude, height, local time, season, and solar and geomagnetic activity levels within the altitude range of 350–420 km. In a paper by Li et al. [2013], the technique of Grad-Shafranov reconstruction is reformulated into an inverse boundary value problem for Laplace's equation on a circle by introducing a Hilbert transform between the normal and tangent component of the boundary gradients. We thank AGU for bringing out this JGR Space Physics special section based on the papers presented in the session ST06 at the joint AOGS-AGU (WPGM) general assembly held in Singapore during 13–17 August 2012.