Mountains versus valleys: semiannual variation of geomagnetic activity Export

@article{citeulike:227621, abstract = {The semiannual variation in geomagnetic activity is generally attributed to the Russell-McPherron effect. In that picture, enhancements of southward field B\_{S} near the equinoxes account for the higher geomagnetic activity in March and September. In a contrary point of view, we argue that the bulk of the semiannual variation results from an equinoctial effect (based on the {theta} angle between the solar wind flow direction and Earth's dipole axis) that makes B\_{S} coupling less effective (by \~{}25\% on average) at the solstices. Thus the semiannual variation is not simply due to "mountain building" (creation of B\_{S}) at the equinoxes but primarily from "valley digging" (loss of coupling efficiency) at the solstices. We estimate that this later effect, which clearly reveals itself in the diurnal variation of the <i>am</i> index, is responsible for \~{}65\% of the semiannual modulation. The characterstic imprint of the equinoctial hypothesis is also apparent in hourly/monthly averages of the time-differented <i>DST</i> index and the <i>AE</i> index.}, author = {Cliver, E. W. and Kamide, Y. and Ling, A. G.}, citeulike-article-id = {227621}, journal = {Journal of Geophysical Research}, keywords = {aa, ae, am, coupling\_function, geophysical\_indices, magnetosphere, seasonal\_variability}, month = {February}, pages = {2413--2424}, posted-at = {2005-06-14 17:01:42}, priority = {0}, title = {Mountains versus valleys: semiannual variation of geomagnetic activity}, volume = {105}, year = {2000} }

TY - JOUR ID - citeulike:227621 L3 - citeulike-article-id:227621 N2 - The semiannual variation in geomagnetic activity is generally attributed to the Russell-McPherron effect. In that picture, enhancements of southward field B_{S} near the equinoxes account for the higher geomagnetic activity in March and September. In a contrary point of view, we argue that the bulk of the semiannual variation results from an equinoctial effect (based on the {theta} angle between the solar wind flow direction and Earth's dipole axis) that makes B_{S} coupling less effective (by ~25% on average) at the solstices. Thus the semiannual variation is not simply due to "mountain building" (creation of B_{S}) at the equinoxes but primarily from "valley digging" (loss of coupling efficiency) at the solstices. We estimate that this later effect, which clearly reveals itself in the diurnal variation of the <i>am</i> index, is responsible for ~65% of the semiannual modulation. The characterstic imprint of the equinoctial hypothesis is also apparent in hourly/monthly averages of the time-differented <i>DST</i> index and the <i>AE</i> index. JF - Journal of Geophysical Research EP - 2424 TI - Mountains versus valleys: semiannual variation of geomagnetic activity VL - 105 SP - 2413 KW - aa KW - ae KW - am KW - coupling_function KW - geophysical_indices KW - magnetosphere KW - seasonal_variability AU - Cliver, EW AU - Kamide, Y AU - Ling, AG PY - 2000/02// ER -