Interplanetary scintillation observations of the solar wind disappearance event of May 1999

摘要: [1] We report extensive interplanetary scintillation (IPS) observations of the solar wind during period centered around 11 May 1999, when Earth was engulfed by a region with unusually low densities (<1 cm−3) and velocities (<350 km s−1). IPS Ooty Radio Telescope (ORT), operating at 327 MHz, probe inner heliosphere along large number closely spaced lines sight over heliocentric distance range 0.2 to 1.0 AU, daily, rate about 150 sources in course 10 hours. Using these observations, southern half monitored everyday between 3 16 1999. The data show that were globally subdued, having started subsiding from itself different parts heliosphere. This accompanied noticeable decrease velocity general also. also reveal small subset lying west Sun steep drop inferred immeasurably amounts on 11th May. actual morphology subsidence event, our is shown be “void-within-a-void”. role polar magnetic field reversal taking place Carrington rotations 1947–1954, which may have played key generating examined. To best knowledge this first time sustained levels been recorded for such long part Some possible signatures high energy “strahl” electrons period.