Observations of plasma density structures in association with the passage of traveling convection vortices and the occurrence of large plasma jets

We report important results of the first campaign specially designed to obs erve the formation and the initial convection of polar cap patches. The pri ncipal instrumentation used in the experiments comprised the EISCAT, the So ndrestrom, and the Super DARN network of radars. The experiment was conduct ed on February 18, 1996 and was complemented with additional sensors such a s the Greenland chain of magnetometers and the WIND and IMP-8 satellites. T wo different types of events were seen on this day, and in both events the Sondrestrom radar registered the formation a:nd evolution of large-scale de nsity structures. The first event consisted of the passage of traveling con vection vortices (TCV). The other event occurred in association with the de velopment of large plasma jets (LPJ) embedded in the sunward convection par t of the dusk cell. TCVs were measured, principally, with the magnetometers located in Greenland, but were also confirmed by the line-of-sight velocit ies from the Sondrestrom and SuperDARN radars. We found that when the magne tic perturbations associated with the TCVs were larger than 100 nT, then a section of the high-latitude plasma density was eroded by a factor of 2. We suggest that the number density reduction was caused by an enhancement in the O+ recombination due to an elevated T-i, which was produced by the much higher frictional heating inside the vortex. The large plasma jets had a c onsiderable (> 1000 km) longitudinal extension and were 200-300 km in width . They were seen principally with the Sondrestrom, and SuperDARN radars. En hanced ion temperature (T-i) was also observed by the Sondrestrom and EISCA T radars. These channels of high Ti were exactly collocated with the LPJs a nd some of them with regions of eroded plasma number density. We suggest th at the LPJs bring less dense plasma from later local times. However, the re cent time history of the plasma flow is important to define the depth of th e density depletion. Systematic changes in the latitudinal location and in the intensity of the LPJs were observed in the 2 min time resolution data o f the SuperDARN radars. The effect of the abrupt changes in the LPJs locati on is to create regions containing dayside plasma almost detached from the rest of the oval density. One of these density features was seen by the Son drestrom radar at 1542 UT. The data presented here suggest that two plasma structuring mechanisms (TCVs and LPJs) can act tens of minutes apart to pro duce higher levels of density structures in the near noon F-region ionosphe re.