Do Hot Flow Anomalies Cause Dramatic Effects on the Entire Magnetosphere?

International audience; Hot flow anomalies (HFAs) are nonlinear structures upstream of Earth's bow shock. Two important properties associated with HFAs are (1) the solar wind (SW) mean flow slows down and deviates substantially and (2) the temperature of the plasma increases in the structure. To understand what could cause these two feffects, the Cluster plasma ion experiment was reconfigured in 2010 and 2011 to sample 3D distributions of the SW and backstreaming particles with spin period time resolution (4s). The new data show the SW beam in HFAs is persistent and the slowdown and deviation of the bulk flow is due to reflected particles canceling the SW beam when computing moments. Data show the SW beam is present throughout the entire HFA event maintaining a nearly constant beam velocity and temperature. Our observations are not consistent with the suggestion that HFAs can cause dramatic effects on the entire magnetosphere driving large variations in the motion and location of the magnetopause.