Find in Library

This work attempts to fill a gap in comparative studies of upstream-generated Pc3–4 waves and broad band ULF noise observed at cusp latitudes. We performed a statistical analysis of the spectral properties of three years of cusp-latitude ground magnetometer data, finding that the average daytime Pc3–4 spectra are characterized by two principal components: an upstream-related band-limited enhancement (<i>‘signal’</i>) and a power-law background (<i>‘noise’</i>) with <i>S(f ) <font face="Symbol">a</font>&nbsp; f ^-4 </i>. Based on this information we developed an algorithm allowing for the deconvolution of these two components in the spectral domain. The frequency of the signal enhancement increases linearly with IMF magnitude as <i>f </i>[mHz] <font face="Symbol"><u>~</u> </font>4.4 | <i>B</i>_IMF | [nT], and its power maximizes around IMF cone angles <i><font face="Symbol">q</font>_xB</i> <u>~</u> 20 and 160° and at 10:30–11:00 MLT. Both spectral components exhibit similar semiannual variations with equinoctial maxima. The back-ground <i>noise</i> power grows with increasing southward <i>B_z </i>and remains nearly constant for northward <i>B_z</i> . Its diurnal variation resembles that of Pc5 field-line resonance power, with a maximum near 09:00 MLT. Both the band-limited <i>signal</i> and broad band <i>noise</i> components show power-law growth with solar wind velocity <font face="Symbol">a </font><i>V</i> ^5.71_sw and <font face="Symbol">a </font><i>V</i> ^4.12_sw, respectively. Thus, the effective <i>signal</i>-to-<i>noise</i> ratio increases with in-creasing <i>V_sw</i>. The observations suggest that the noise generation is associated with reconnection processes.<br><br><b>Key words.</b> Magnetospheric physics (magnetopause, cusp, and boundary layers; MHD waves and instabilities; solar wind magnetosphere interactions)