Continuous ground-based observations of the dayside aurora provide important information, complementary to the in situ measurements from satellites, on plasma transport and electromagnetic coupling between the magnetosheath and the magnetosphere. In this study, observations of the polar cusp/dayside oval aurora from Svalbard and simultaneous observations of the nightside aurora from Poker Flat, Alaska, and the interplanetary magnetic field from satellites are used to identify the ionospheric signatures of plasma transfer from the solar wind to the magnetosphere. The characteristics of motion, spatial scale, time of duration, and repetition frequency of certain dayside auroral forms which occur at the time of large-scale oval expansions (interplanetary magnetic field Bz < 0) are observed to be consistent with the expected optical signatures of plasma transfer through the dayside magnetopause boundary layer, associated with flux transfer events. Similarly, more large-scale (time and space) events are tentatively explained by the quasi steady state reconnection process. 1. 10,063 10,064 SANDHOLT ET AL.: MAGNETOPAUSE PLASMA TRANSFER AND DAYSIDE AURORA geomagnetic coordinates of these stations, Ny ,•lesund (NY•) and Longyearbyen (LYR) are 75.4 ø, 131.4 ø (NY•) and 74.4 ø, 130.9 ø (LYR). By this technique the dayside auroras can be observed within the range •69ø-80 ø geomagnetic latitude at midwinter. Local magnetic noon and solar noon at the recording sites occur at •0830 and • 1100 UT, respectively. An all-sky imaging photometer is operated at Ny fklesund. This instrument has a 155 ø field of view (spanning 1200 km for F-region emissions) and a threshold sensitivity of •30 R at 630 nm [cf. Carlson, 1984]. This instrument and an all-sky camera at LYR [Deehr et al., 1980] provided important supplementary information relative to the meridian profiles recorded by the scanning photometers. Dayside geomagnetic disturbances were recorded by standard magnetometers at the three Svalbard stations: Ny •lesund, Hornsund (73.5 ø geomagnetic latitude), and BjOrnOya (71.

The spectrographic imagers on the MSX satellite have made the first observations of the middle ultraviolet spectra (200–315 nm) of polar mesospheric clouds (PMCs). Dividing the PMC spectra by the solar spectrum yields a scattering spectrum expressible as a matrix‐vector formalism of Mie scattering functions and the particle distribution. Using this formalism, PMC particle distributions are related to the observed scattering spectrum. The scattering spectrum always exhibits a peculiar “hump” at ∼260 nm that cannot be explained by any effect other than the particle distribution. A lognormal distribution of small particles (mode ∼ 50 nm) produces the overall shape of the spectrum but not the “hump.” Although not unique, a simple bimodal distribution of small particles (r ∼ 50 nm) and large particles (r ∼ 200 nm) describes the scattering spectrum and its hump very well. The clouds may therefore consist of two different populations, as suggested by some models of the clouds. Numerically, smaller particles dominate by about 10:1, but the larger particles strongly influence the scattering spectrum.

[1] A new approach to optical remote sensing of the Earth's atmosphere using a combination of extinctive and refractive stellar occultation measurements is presented. In this combined method, spectrographic imagers are used to measure the wavelengthdependent atmospheric extinction of starlight while a co-aligned imager is used to measure the atmospheric refraction along the same line of sight. By simultaneously measuring both the refraction and extinction of the starlight, the composition-dependent extinction measurements can more accurately probe the Earth's lower atmosphere, where refraction effects are significant. The refraction measurements provide the bulk atmospheric properties and the actual light path through the atmosphere, both of which are necessary to correctly infer the total extinction in the refractive regime. The technique is demonstrated on a proof-of-concept basis using data from the Ultraviolet and Visible Imagers and Spectrographic Imagers (UVISI) on the Midcourse Space Experiment (MSX) satellite. These preliminary results show that the combined approach has the potential to be a powerful, self-calibrating method for remotely sensing the Earth's atmosphere in general and for the determination of ozone profiles in the stratosphere and upper troposphere in particular.

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Auroral‐height measurements were made during a 5‐month period of the IQSY using meridian scanning photometers at three stations spanning the auroral zone on the same dipole meridian. The measurements were restricted to stable homogeneous auroral arcs, which usually occur during quiet times between substorms. They refer to the height of maximum volume emission rate of λ5577 [O I] that in these arcs was found to coincide with that of λ4278 (N2+ first negative). The height of maximum emission of λ4278 is directly related to the characteristic energy of the precipitated auroral electrons. Sufficient triangulation data were obtained (1152 points) to allow a separation of the effects of local time and latitude, which are normally related through the diurnal motion of the auroral oval. Interpreted in terms of the precipitated electrons, the photometric data reveal that the distribution of characteristic electron energy has two components: (1) at any local time during the night the electron energy increases with decreasing latitude, and (2) at every latitude the electron energy increases with increasing time throughout the night. The flux of the precipitated electrons generally increases with time and decreasing latitude. It appears that stable homogeneous auroral arcs observed during quiet times between substorms are manifestations of convective particle motion in the magnetosphere and not of local acceleration mechanisms. This study suggests several extensions or improvements of current theories of magnetospheric convection that would allow a more quantitative comparison between the theoretical models and experimental results.