Abstract

Abstract. A time and frequency-domain analysis is made of the effects of averaging and sampling methods used for con-structing magnetic-observatory hourly data values. Using 1-min data as a proxy for continuous, geomagnetic variation, we construct synthetic hourly values of two standard types: instantaneous “spot ” measurements and simple 1-h “boxcar” averages. We compare these average-sample types with oth-ers: 2-h average, Gaussian, and “brick-wall ” low-frequency-pass. Hourly spot measurements provide a statistically unbi-ased representation of the amplitude range of geomagnetic-field variation, but as a representation of continuous field variation over time, they are significantly affected by alias-ing, especially at high latitudes. The 1-h, 2-h, and Gaussian average-samples are affected by a combination of amplitude distortion and aliasing. Brick-wall values are not affected by