Risr-N Observation of the Characteristics of Polar Cap Patches and Implication for Patch Formation Mechanism

Tuesday, 16 December 2014
Shasha Zou1, Sina Y. Tafti1, Aaron J Ridley1, Mark Moldwin1 and Michael J Nicolls2, (1)University of Michigan, Ann Arbor, MI, United States, (2)SRI International, Menlo Park, CA, United States
Polar cap patches are islands of high F-region plasma density within the polar cap and they are of significant practical importance because of the associated plasma instabilities and scintillations in GPS signals. An automatic algorithm has been developed to identify the polar cap patch using observations from the Resolute Bay Incoherent Scatter Radar North Face (RISR-N). In addition, a statistical study of the characteristics of patches identified has been carried out, including the occurrence rate distributions by month, UT/MLT, and IMF orientation. A superposed epoch analysis of the ionospheric vertical profiles of patches has also been performed for the Feb. 1-8, 2011 radar run. Comparing with the averaged vertical profiles of all times, it is found that the patch plasma temperatures are higher above ~420 km, the vertical flow velocity are enhanced downward between ~350-550 km and upward above ~550 km. When patches observed within the 2 hours of MLT around noon are selected, i.e. closer to the location where they are generated, the patch electron temperature is lower than average between ~350-420 km and higher above ~420 km. We suggest that this is due to the combined effect of the coming-in cooler SED plume temperature and the heating process at cusp by soft particle precipitation. High-resolution GITM runs are used to model several intervals where patches are observed most comprehensively within the data.