Large-Density Heliospheric Plasma Sheets Recorded by the Wind Spacecraft Between 1995 and 2017

The heliospheric plasma sheet (HPS) is a region of enhanced plasma density that surrounds the heliospheric current sheet (HCS). At 1 AU the median value of the (peak) density of the HPS is $\sim$18 cm$ ^{-3}$, about 3-4 times of the typical solar wind density. An important aspect of the HPS in space weather is its geoeffectiveness. When the HPS impinges and compresses Earth's magnetosphere, geomagnetic activity can result. The effect increases roughly with the increasing density enhancements. This study focuses on some unusual large-density (>50 cm$ ^{-3}$) HPS events, as they are highly geoeffective. We have identified $\sim$120 large-density HPS events recorded by the Wind spacecraft from 1995 to 2017. It is found that most of these large-density HPS events are associated with interplanetary shocks or pressure pulses, suggesting that large-density HPS events result from IP shock compression. We will present the details of our analysis results and discuss possible mechanisms in the context of shock-HPS interactions. * Work of CCW was supported partially by NASA 80HRTR19T0062 and 80HQTR18T0023 grants and the Chief of Naval Research.