Recent observations of auroral kilometric radiation (AKR) reported by James [1980] from the ISiS 1 data shows that in the generation region the AKR is downcoming, propagating at an angle between 60 ø and 90 ø with respect to the magnetic field, and that the local plasma frequency is much less than the local electron gyrofrequency. James points out that the theories of Wu and Lee [1979] and Roux and Pellat [1979] are

The power delivered by the solar wind dynamo to the open magnetosphere is calculated based on the concept of field line reconnection, independent of the MHD steady reconnection theories. By recognizing a previously overlooked geometrical relationship between the reconnection electric field and the magnetic field, the calculated power is shown to be approximately proportional to the Akasofu‐Perreault energy coupling function for the magnetospheric substorm. In addition to the polar cap potential, field line reconnection also gives rise to parallel electric fields on open field lines in the high‐latitude cusp and the polar cap regions.

It is suggested that the flux transfer events (FTE's) observed by ISEE satellites can be the result of multiple X‐line reconnection at the dayside magnetopause, which may be caused by the development of a tearing instability. In the presence of the y‐component of the magnetic field (By) in the transition region of the magnetopause, the tearing instability leads to the interconnection of the geomagnetic field lines and the interplanetary field lines, and hence to the occurrence of FTE's. Twisted field lines and field‐aligned currents are formed as a consequence of the tearing instability. The flow direction of the field‐aligned currents depends on By and the results are found to be consistent with satellite observations.

[1] We report the global transient luminous event (TLE) distributions and rates based on the Imager of Sprites and Upper Atmospheric Lightning (ISUAL) experiment onboard the FORMOSAT-2 satellite. ISUAL observations cover 45°S to 25°N latitude during the northern summer and 25°S to 45°N latitude during the northern winter. From July 2004 to June 2007, ISUAL recorded 5,434 elves, 633 sprites, 657 halos, and 13 gigantic jets. Surprisingly, elve is the dominant type of TLEs, while sprites/halos are a distant second. Elve occurrence rate jumps as the sea surface temperature exceeds 26 degrees Celsius, manifesting an ocean-atmosphere-ionosphere coupling. In the ISUAL survey, elves concentrate over the Caribbean Sea, South China Sea, east Indian Ocean, central Pacific Ocean, west Atlantic Ocean, and southwest Pacific Ocean; while sprites congregate over central Africa, Japan Sea, and west Atlantic Ocean. The ISUAL experiment observed global rates of 3.23, 0.50, 0.39, and 0.01 events per minute for elves, sprites, halos, and gigantic jets, respectively. Taking the instrumental detection sensitivity and the restricted survey area into account, the corrected global occurrence rates for sprites and elves likely are a factor of two and an order of magnitude higher, respectively. ISUAL observations also indicate that the relative frequency of high peak current lightning (>80 kA) is 10 times higher over the oceans than over the land. On the basis of the corrected ISUAL elve global occurrence rate, the total electron content at the lower ionosphere above elve hot zones was computed to be elevated by more than 5%.

Transient luminous events in the atmosphere, such as lighting-induced sprites and upwardly discharging blue jets, were discovered recently in the region between thunderclouds and the ionosphere. In the conventional picture, the main components of Earth's global electric circuit include thunderstorms, the conducting ionosphere, the downward fair-weather currents and the conducting Earth. Thunderstorms serve as one of the generators that drive current upward from cloud tops to the ionosphere, where the electric potential is hundreds of kilovolts higher than Earth's surface. It has not been clear, however, whether all the important components of the global circuit have even been identified. Here we report observations of five gigantic jets that establish a direct link between a thundercloud (altitude approximately 16 km) and the ionosphere at 90 km elevation. Extremely-low-frequency radio waves in four events were detected, while no cloud-to-ground lightning was observed to trigger these events. Our result indicates that the extremely-low-frequency waves were generated by negative cloud-to-ionosphere discharges, which would reduce the electrical potential between ionosphere and ground. Therefore, the conventional picture of the global electric circuit needs to be modified to include the contributions of gigantic jets and possibly sprites.

In our previous model for the lithosphere-atmosphere-ionosphere coupling, the background magnetic field was assumed to be perpendicular to the horizontal plane. In the present paper, we improve the calculation of currents in the atmosphere by solving the current density J directly from the current continuity equation ∇ • J = 0. The currents in the atmosphere can be solved for any arbitrary angle of magnetic field, i.e., any magnetic latitude. In addition, a large ratio (~10) of Hall to Pedersen conductivities is used to generate a large Hall electric field. The effects of atmospheric currents and electric fields on the ionosphere with lithosphere current source located at magnetic latitudes of 7.5°, 15°, 22.5°, and 30°are obtained. For upward (downward) atmospheric currents flowing into the ionosphere, the simulation results show that the westward (eastward) electric fields dominate. At magnetic latitude of 7.5°or 15°, the upward (downward) current causes the increase (decrease) of total electron content (TEC) near the source region, while the upward (downward) current causes the decrease (increase) of TEC at magnetic latitude of 22.5°or 30°. The dynamo current density required to generate the same amount of TEC variation in the improved model is found to be smaller by a factor of 30 as compared to that obtained in our earlier paper. We also calculate the ionosphere dynamics with imposed zonal westward and eastward electric field based on SAMI3 code. It is found that the eastward (westward) electric field may trigger one (two) plasma bubble(s) in the nighttime ionosphere.

[1] Electron energies and the strength of electric fields in sprites are deduced for five selected events, which were recorded by the space-borne instrument called ISUAL (Imager of Sprites and Upper Atmospheric Lightning; a payload on the FORMOSAT-2 satellite). From the derived peak intensity ratios of spectrophotometer channel 2 (centered at 337 nm) and channel 3 (centered at 391.4 nm) of these sprites, the average and characteristic electron energies were found to be in the range of 6.2-9.2 eV and 4.5-6.5 eV, respectively. The estimated E/N at 40-60 km is 243-443 Td and the strength of the electric field is 2.1-3.7 times that of the atmosphere breakdown E-field at these altitudes. The inferred electron energies and the strength of electric fields are about two times higher than those inferred from ground campaigns. However, they are consistent with the prediction of the sprite streamer model.

[1] The electromagnetic pulses (EMP) from tropospheric lightning produce transient luminous events (TLEs), known as elves, in the 80-90 km region above the lightning. The luminosity is evidence that the EMP carries sufficient electric field to excite optical emissions at these altitudes; however, it is still unknown whether the field is sufficient to ionize the atmosphere. The first multiwavelength, quantitative observatory on a free-flying satellite dedicated to observing TLEs, the Imager of Sprites and Upper Atmospheric Lightning (ISUAL) instrument on FORMOSAT-2, formerly called ROCSAT-2, confirmed that a significant number of lightning events are accompanied by elves. The instrument consists of a low light level imager and a set of multichannel photometers. In a few cases where the lightning occurred beyond the solid Earth limb, pure spectral measurements of the elves were obtained. Here we analyze such an event and show that the elves contained significant 391.4 nm emission of the N 2 + ion. This is clear evidence that ionization takes place in elves. The ratio of cross sections for N 2 ionization and the production of the upper state of 391.4 nm emission is not a constant for low-energy electrons found in TLEs. We attempted to find this ratio by comparing our photometric measurements of the TLE produced emissions to theoretically derived emission intensities. The electron energy distribution and the ratios of the modeled N 2 Lyman-Birge-Hopfield (LBH) and the N 2 + first negative to the second positive were computed as a function of the reduced electric field. From these ratios it was possible to obtain the reduced electric field from the ratios. We estimated that the reduced electric field, which characterizes the local electron energy distribution, was >200 Td. We also made comparisons of the theoretically derived intensities to our measurements of the N 2 + first positive and Lyman-Birge-Hopfield (LBH) band emission in the elves. On the basis of the ratio between the N 2 + first negative emission and the time-integrated ionization production, we estimate that the elves produced an average electron density of 210 electrons cm À3 over a large (165 km diameter) circular region having an assumed 10 km altitude extent. These observations indicate that thunderstorms are a significant source of ionization in the low-to midlatitude nighttime D region.