A PRACTICAL EXAMPLE OF LOW-FREQUENCY TREND REMOVAL - RESEARCH NOTE

Three different 'classical' methods of removing low-frequency trends a re used to detrend some instrumental data, and their effect is evaluat ed. The examples given here highlight problems that may occur whenever detrending is necessary. The trend present in the data arises from th e passage of synoptic weather systems over the Antarctic during the op eration of the instrument. The resultant signal varies over a period o f hours. This contrasts with the phenomenon to be studied (atmospheric gravity waves), which have periods of a few tens of minutes at most a nd amplitudes typically one or two orders of magnitude smaller than fo r synoptic systems. The trend removal procedure is relevant to many mo re situations than the analysis of meteorological pressure data.