Abstract. The U.S. Department of Energy funded the development of the multifilter rotating shadowband radiometer (MFRSR) as part of the Atmospheric Radiation Measurement (ARM) program. This seven-channel radiometer began operation at the first ARM site in 1992 and at the Department of Energy Quantitative Links (QL) sites in the fall of 1991; three of the QL sites continue to operate, although this program was discontinued after 1995. This paper describes the use of the MFRSR in acquiring aerosol optical depth data, including the in-field calibration procedure and a partial validation of this process. Multiyear measurements of aerosol optical depth from three of the sites indicate similar phasing of seasonal and interannual changes, but with notable differences in the magnitude of the aerosol optical depth. Published papers that use these aerosol data are highlighted, and public access to these and future data sets for scientific studies are explained.

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Measurements are reported in this paper which indicate the nature of the enhancement of the stratospheric aerosol layer by month for the first full year following the Spring 1982 eruptions of El Chichon. The aerosol optical depths as a function of wavelength are obtained by differencing mean monthly values obtained before and after the eruptions. The first enhancement above background was detected in September 1982. The inverted size distributions indicate a steady increase to larger mean size particles each month with a radius near 0.6 micrometers during the last reported month of March 1983. This size is considerably larger than that which is generally assumed for the sulfuric acid aerosols which form following an eruption.

Particle flux data acquired by the ISEE 1 and 2 spacecraft reveal many order of magnitude changes within the magnetopause boundary layer that occur during less than 1/4 s of time. These changes define small‐scale particle structures, or microstructures within the region, many of which are apparently inclusions of plasma from adjacent regions. Particle structures resolved by the high time resolution data include groups with periods as short as 0.375 s. An estimate is derived for the motion of the microstructures with respect to an oscillatory inner boundary for four afternoon sector boundary layer crossings by measuring interspacecraft time differences as the features propagate past the satellites. On average the microstructures move toward the tail of the magnetosphere in concert with the wavy large‐scale inner boundary. Furthermore, the orientations of the edges of the structures maintain an aspect similar to that of the boundary. These characteristics are expected for magnetohydrodynamic plasma flows that generate velocity due to velocity shear stresses.

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