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In this study, we investigate two global\udclimatological data sets; the occurrence rate of Equatorial Spread-F\ud(ESF), associated with\udequatorial plasma irregularities,\udat ~400 km altitude\udobtained from CHAMP observations, and the evening\udequatorial vertical plasma drift, vz,\udfrom ROCSAT-1 measurements.\udFirst, as retrieved for a solar flux level of F10.7=150,\udthe longitudinal variation of the two independently derived\udquantities correlates between 84% and 93%\udin the seasons December solstice, equinox and June solstice.\udThe highest correlation is found for the solstice seasons\udwhen vz is integrated over local time\udaround the prereversal enhancement (PRE) and displaced\ud6° towards east.\udThe integrated vz is a suitable estimate of the ionospheric height\udat the time just after the PRE and the 6°\uddisplacement is consistent with ESF eastward drift during\ud2 h which is assumed between creation and detection at satellite altitudes.\udSecond, our analyses reveal a global threshold vz which is required to\udobserve ESF at satellite altitudes. This threshold depends linearly\udon solar flux with correlations of 97%.\udBoth results bring global evidence on the linear relations between ESF\udand the vertical plasma drift\udwhich have been proven only by local observations\udso far.\ud\ud \ud\udThis paper includes the first global map of the\udseasonal/longitudinal variation of the ESF occurrence rate over\udlocal time being valid for high solar flux years 2001–2004.\udThe map reveals, e.g. a longitudinal dependence of the persistence of the\udplasma irregularities\udindicating that longitude dependent mechanisms other than\udthe PRE determine the ESF lifetime

Relation between the occurrence rate of ESF and the equatorial vertical plasma drift velocity at sunset derived from global observations