| Popis: |
We analize magnetosheath Cluster data from 2007 and 2008, included in FP7 STORM database (http://www.storm-fp7.eu). We identify magnetosheath jets based on a procedure that searches for significant departures of the local dynamic pressure from an average value. The latter is estimated from a running window spanning 20 minutes of data. The selection criterion is applied on Cluster 3 dataset and identifies 955 magnetosheath jets, with a notable difference between 2007 and 2008 (352 versus 603 events). The statistical analysis of the plasma bulk velocity, density, temperature, plasma beta, magnetic field and radial distance of the jets provides interesting elements for understanding their dynamics. There is evidence for deceleration of jets with decreasing distance from the Earth; interestingly, this trend manifests more clearly for jets detected in 2008. More jets are found in the dawn than in the dusk flank, for 2007 and 2008. A comparison with the plasma parameters of the driver, the IMF Bz and the solar wind dynamic pressure from OMNI database, indicate there is no preference in terms of Bz polarity. The distribution of jet magnetic field, temperature (parallel, perpendicular), dynamic pressure, plasma beta and total speed is symetric when organized as a function of IMF Bz, with one exception, the jet perpendicular temperature and plasma beta. An increased solar wind dynamic pressure seems to correlate to higher values of the jet density but not velocity. We discuss these results in the context of previous similar magnetosheath jet analysis performed on MMS and THEMIS data. |
