Information on solar irradiance at wavelengths below 185 nm, observed by the EUVS experiment on the AE‐E satellite over the entire development of the present sunspot cycle 21, is important to many investigations of planetary thermospheres and ionospheres. Strictly observational information is generally lacking in both the completeness and the spectral detail required by the more advanced study programs. Therefore, it has been necessary also to develop computer models in connection with fully detailed compilations of an appropriate reference spectrum. Our selection of appropriate forms of effective publication has been difficult for various reasons. Recognizing that full reproduction of our various lists of observational, reference, and model data in scientific journals would be impracticable, we started a more or less informal procedure of timely release of information to a limited number of particularly interested colleagues. With the present letter, we hope to mitigate at least some of the dissatisfactory aspects of this procedure.

This is the first analysis, using a statistically significant data set, of the morphological dependence of the presence, orientation, and motion of stable sunaligned polar cap arcs upon the vector interplanetary magnetic field (IMF). For the one winter season analyzed we had 1392 all-sky 630.0-nm images of 2-min resolution containing a total of 150 polar cap arcs, all with corresponding values of the IMF as measured by IMP 8 or ISEE 2. After demonstrating an unbiased data set with smooth normal distributions of events versus the dimensions of time, space, and IMF component, we examine IMF dependencies of the properties of the optical arcs. A well-defined dependence for B z is found for the presence/absence of stable Sun-aligned polar cap arcs. Consistent with previous statistical studies, the probability of observing polar cap aurora steadily increases for larger positive values of B z , and linearly decreases when B z becomes more negative. The probability of observing Sun-aligned arcs within the polar cap is determined to vary sharply as a function of the arc location; arcs were observed 40% of the time on the dawnside and only 10% on the duskside. This implies an overall probability of at least 40% for the whole polar cap. 20% of the arcs were observed during "southward IMF conditions," but in fact under closer inspection were found to have been formed under northward IMF conditions; these "residual" positive B z arcs had a delayed residence time in the polar cap of about what would be expected after a north to south transition of B z . A firm dependence on By is also found for both the orientation and the dawn-dusk direction of motion of the arcs. All the arcs are Sun-aligned to a first approximation, but present deviations from this orientation, depending primarily upon the location of the arc in corrected geomagnetic (CG) coordinates. The arcs populating the 06-12 and the 12-18 quadrants of the CG coordinate system point toward the cusp. The By dependency of the arc alignment is consistent with a cusp displacement in local time according to the sign of B We found that the arc direction of motion depended both on By and the arc ß y' location within the polar cap. For a given value of By, two well-defined regions (or cells) exist. Within each cell the arcs move in the same direction toward the boundary between the cells. The arcs located in the duskside move dawnward; those in the dawnside move duskward. The relative size of these dusk and dawn regions (or cells) are controlled by the magnitude of By. This persistent dusk-dawn motion of the polar cap arcs is interpreted in terms of newly open flux tubes entering the polar cap and exerting a displacement of the convective cells and the polar cap arcs that are embedded within them. was realized that this type of aurora only developed at latitudes poleward of the auroral oval [Weill, 1958; Denholm and Bond, 1961; Davis, 1960]. A few years later it was discovered that the Sun-aligned arcs preferentially developed when the interplanetary magnetic field (IMF) point...

[1] This paper studies dayside shock aurora forms and their variations observed by the ground-based all-sky imager (ASI) in Svalbard on 30 November 1997. The interplanetary shock arrived at Earth when Svalbard was at $1120 magnetic local time. The ASI detected an auroral intensification by a factor of 2 or more in both green and red line emissions within 5 min after the shock arrival. The intensified green emissions were mainly diffuse aurora on closed field lines. They were latitudinally below and adjacent to the red aurora, which was mainly in the form of arcs and beams along the magnetic east-west direction. The diffuse aurora expanded equatorward and eastward, and its intensity exceeded the red arcs that were at $5 kR. We confirmed that the eastward propagating diffuse aurora was actually moved antisunward along the oval, which suggests that the antisunward propagating shock aurora seen in space is mainly diffuse aurora. The intense diffuse aurora could be caused by wave instabilities led by a temperature anisotropy and/or caused by an enlarged loss cone. After the shock arrival, the detected low-latitude boundary of the cusp moved equatorward at a speed of $18 km min À1 . As a result, the cusp meridional width was doubled from $0.8°to 1.6°in latitude in 10 min. This finding implies that a low-latitude reconnection occurred during the compression. In this study the auroral signatures and speculated mechanisms are consistent with those revealed by in situ particle and wave observations from FAST and DMSP.

During weak Bz or Bz < 0 conditions, antisunward convection dominates the central polar cap as shown by Digisonde drift measurements. During these conditions, polar cap F layer patches are observed routinely to drift antisunward within the overall plasma convection. A study is presented which compares patch motion derived from 630.0‐nm all‐sky intensified camera (ASIC) images taken at Qaanaaq, Greenland (87° CGL) with simultaneously obtained Digisonde drift measurements. During four periods of the winter 1989/1990 43 630.0‐nm patches were identified and followed in their motion across the ASIC field of view. The shape, velocity, and drift direction of the individual patches were determined. The patch motion was then compared with the Digisonde drift measurements. The drift direction is generally antisunward (±25°); both data sets are in excellent agreement, with a typical ±20° scatter around a common central value. The velocity magnitudes from both measurements show considerable variability, but both measurements generally cover the same velocity range. The variations and variability of the velocity magnitude are discussed in the context of simultaneous IMF measurements. Rapid changes in velocity were traced to changes in Bz. Deviations from antisunward of the azimuths of the optical patch drift and the Digisonde drift measurements were controlled by IMF By in agreement with published By control of convection.

LHCf is an experiment dedicated to the measurement of neutral particles emitted in the very forward region of LHC collisions. The physics goal is to provide data for calibrating the hadron interaction models that are used in the study of Extremely High-Energy Cosmic-Rays. This is possible since the laboratory equivalent collision energy of LHC is 10 17 eV. Two LHCf detectors, consisting of imaging calorimeters made of tungsten plates, plastic scintillator and position sensitive sensors, are installed at zero degree collision angle ±140 m from an interaction point (IP). Although the lateral dimensions of these calorimeters are very compact, ranging from 20 mm×20 mm to 40 mm×40 mm, the energy resolution is expected to be better than 6% and the position resolution better than 0.2 mm for γ-rays with energy from 100 GeV to 7 TeV. This has been confirmed by test beam results at the CERN SPS. These calorimeters can measure particles emitted in the pseudo rapidity range η>8.4. Detectors, data acquisition and electronics are optimized to operate during the early phase of the LHC commissioning with luminosity below 10 30 cm −2 s −1 . LHCf is expected to obtain data to compare with the major hadron interaction models within a week or so of operation at luminosity ∼ 10 29 cm −2 s −1 . After ∼10 days of operation at luminosity ∼10 29 cm −2 s −1 , the light output of the plastic scintillators is expected to degrade by ∼10% due to radiation damage. This degradation will be monitored and corrected for using calibration pulses from a laser.