Dynamic Pressure Pulse And The Its Relationship To Geomagnetic Sudden Commencement

Interplanetary is the bridge between the sun and the earth.Dynamic pressure pulse(DPP)is a common small-scale structure in solar wind,which dynamic pressure usually changes obviously in a few minutes.DPP can cause obvious disturbances in the magnetosphere-ionosphere space.Geomagnetic sudden commencement(SC)is one of the geophysical effects of DPP.Automatic detection of DPP based on solar wind observation and a deep understanding of DPP characteristics is important for enriching the cognition of solar wind physical characteristics and improving the ability of space weather early warning.In addition,a deep study of the relationship between SC and DPP is important for understanding the physical process of interaction between solar wind and magnetosphere,further understanding the causes and the characteristics of SC and improving the ability of SC prediction.In this paper,learning from the automatic detection algorithm proposed by Zuo et al(2015),automatic detection of DPP based on WIND satellite is achieved.And more than 10000 DPP events observed between 1994 and 2016 are the objectives.Firstly,the characteristics of the DPP events statistically are analyzed.Secondly,the relationship between DPP and SC is studied seeing that DPP is one of the main causes of SC.Finally,based on the above research,an empirical prediction model is established.SC can be predicted by characteristic parameters of DPP.And the model test is carried out.The results are as follows:1.Based on 11909 DPP events observed between 1994 and 2016,for most(about70.4%)DPP events,the absolute dynamic pressure change is distributed in the range 1.0~ 2.0nPa.The relative dynamic pressure change of the DPP events is distributed in the range 0.2 ~ 2.0 with half(about 54.1%)in the range 0.2 ~ 0.4.The number of the DPP events decreases obviously with the increase of the absolute dynamic pressure change and the relative dynamic pressure change.28.3% of the DPP event's duration time is distributed in the range 150 ~ 210 s.Especially,77.1% of the DPP events are associated with large-scale solar wind disturbance structures,such as interplanetary coronal mass ejections(ICME),corotating interaction region(CIR)and complex projections caused by ICME and/or CIR.And,38.8% of the DPP events are located at the first 1/3 position of large-scale solar wind disturbance structures.In the meanwhile,only 15.1% of the DPP events are located at the final 1/3 positions of large-scale solar wind disturbance structures.Furthermore,the daily frequency of the DPP events is positively related to the solar cycle.2.Analyzing the characteristics of the 330 DPP—SC events,we find:(1)91% of the SC events are associated with the DPP events,and 53% of the SC events are associated with the shocks.This indicates that DPP is the main cause of SC.(2)Compared with the normal DPP events,the DPP events associated with the SC eventsusually have stronger absolute dynamic pressure change and relative dynamic pressure change.And most of the SC-associated DPP events occur at the beginning of the large scale solar wind disturbances.This provides a basis for future research on what kind of DPP is associated with SC.(3)There is an obviously positive relationship between the amplitude of the SC events and the absolute dynamic pressure change as well as the difference of the square root of the dynamic pressure of the DPP events.And,the positive relationship is more obvious when interplanetary magnetic field is southward.The speed of the DPP events has a positive influence on the amplitude of the SC events while the duration of the DPP events has little influence.In addition,the duration,the speed and the difference of the square root of the dynamic pressure of the DPP events have a certain influence on the duration of the SC events.But the relationship between the characteristic parameters of the DPP events and the duration of the SC events is not obvious.3.Based on the statistical analysis result of the DPP—SC events,the experimental forecasting model that predicts the starting time,the amplitude and the duration of SC by using the characteristic parameters of DPP is established.And this model is tested based on the new DPP—SC events observed between February 2011 and 2015.The results show that the prediction of the amplitude of SC is the best.The prediction of the starting time of SC is relatively good while the prediction of the duration of SC is not satisfactory.It is necessary to consider the direction of the DPP events in this prediction model.