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The pulsating-cusp model of the magnetopause is supported by new observations. The magnetopause is the region where the solar wind forms a boundary with earth's magnetosphere, and competing models show it as either continuous or varying such as in a pulsating cusp. Observations using satellite and ground based radar show that auroras in the polar region result from plasmas from the solar wind, fitting the pulsating-cusp model.

Research on low-altitude and ground-based signatures of the cusp/cleft are now generally looked to for important insight into the nature of space plasma processes in the magnetopause and boundary layers. The height distribution of the day-side cusp aurora and the relation between optical emissions and net downward electron energy flux are the main subjects of this paper. These two important characteristics of day-side cusp aurora are still unknown. It is instructive to compare particle flux and optical luminosity because these two quantities should be proportional if the cusp aurora is caused by electron impact, as has been found for nighttime aurora in the oval. Furthermore, there should then be a direct relation between auroral altitudes and particle energy. Based on coordinated auroral observations at Svalbard and Greenland, together with simultaneous, overhead F-9 satellite measurements, these quantities have been evaluated. The main findings can be summarized as follows: i) For quiet conditions, auroral altitudes near 350 km fit the observations best. This is roughly 100 km higher than normally assumed. Only during events when the green auroral line dominated did the height of the 630 nm decrease to 250 km or even below. ii) Within the soft particle regions, where the average energy was less than 250 eV, a conversion factor of approximately 5 kR per 10 to the -3 W m to the -2 was obtained. However, within regions where typical 1.5 keV or more energetic electrons dominated, only equivalent to 1 kR at 630 nm was produced per 10 to the -3 W m to the -2. iii) Due to the difficulties in coordinating ground and satellite measurements, to be sure that the observed aurora is caused by the recorded electrons at the satellite as well as uncertainties in the calibrations, departures from the values listed in point ii above by 50% may probably occur. iv) In addition to particle excitation of 630 nm emission, it is important for future quantitative work to consider additional excitation mechanisms: thermal electron excitation and dissociative recombination emission. While the latter is generally limited to altitudes near 250-300 km, the former is key to emission seen well above 350 km. These findings are discussed in relation to day-side cusp auroral characteristics and the main sources for these optical emissions. They bear on interpretation of cusp auroral signatures and space plasma processes.

North American observations of noctilucent clouds (NLC) in the periods 1964-1977 and 1988-2014 are compared. Between the two study periods there has been no change in the activity profile of the NLC season; nor has there been any trend in NLC incidence. When comparing individual sites, it was determined that at Broadview, Sask. (50.4N 102.6W) and The Pas, Man. (54.0N 101.1W), there were no significant trends in incidence nor brightness. However, in the case of Baker Lake, Nun. (64.3N 96.0W), in 2003-2009 there was marked increase in NLC incidence, but also a decrease in average brightness in 1993-2009 compared with 1967-1977. Brightness data from 1967-1977 indicate that average and maximum NLC brightness increases with increasing latitude. A study of observer detection of NLC of different brightnesses confirms that a significant number of displays are missed because they are too faint for some observers to see; consequently, when comparing NLC incidence between two periods, it may be preferable to compare only numbers of bright displays. [ABSTRACT FROM AUTHOR]