Poynting Flux in the Dayside Polar Cap Boundary Regions (cusp & LLBL) at Different Altitudes

Wednesday, 12 July 2017: 10:40
Furong Room (Cynn Hotel)
Yue Deng1, Yang Lu1, Cheng Sheng2, Liam M Kilcommons3, Delores Knipp4, Quanqi Shi5, Xiaochen Guo5, Hui Zhang6, Donghe Zhang7 and Qiugang Zong8, (1)University of Texas at Arlington, Arlington, TX, United States, (2)High Altitude Observatory, Boulder, CO, United States, (3)University of Colorado, Boulder, CO, United States, (4)University of Colorado at Boulder, Boulder, CO, United States, (5)Shandong University at Weihai, Weihai, China, (6)University of Alaska Fairbanks, Physics Department & Geophysical Institute, Fairbanks, AK, United States, (7)Peking University, Beijing, China, (8)Peking University, School of Earth and Space Sciences, Beijing, China
Abstract:
With the launch of Defense Meteorological Satellite Program (DMSP) and Cluster spacecrafts, calculating Earth-directed Poynting flux at both satellite altitudes became possible, which provides the capability to compare the energy inputs in the polar cap regions at different altitudes. The estimation of Poynting flux from DMSP satellite observations shows that the cusp region may or may not have substantial downward Poynting flux. Our analysis of DMSP F15 satellite (800–850 km) data during 2000-2004 reveals that 49.6% of 1999 cusp crossings showed significant downward Poynting flux (S > 10 mW/m2) in the cusp, 84.2% of the crossings had strong downward Poynting flux (S > 3 mW/m2), and only 4.2% of the crossings did not show clear Poynting flux (S < 1 mW/m2). The dependence of Poynting flux in the cusp on the magnitude of IMF in the Y-Z plane has been studied for four different IMF clock angles and averagely the Poynting flux is largest when By is dominant and positive. In the lower latitude boundary layer (LLBL) region, 33% of 17304 LLBL crossings showed significant downward Poynting flux, 68% of the crossings had strong downward Poynting flux, and only 13% of the crossings did not show clear Poynting flux. On average, Poynting flux in LLBL is smaller than that in the cusp. Similar data processing has been conducted with Cluster data and the calculated Poynting flux has been mapped down to the DMSP satellite altitudes. In 94 Cluster (2−6 Re) cusp crossings in 2001-2004, 40% crossings observed significant downward Poynting flux, 72% showed strong downward Poynting flux, and 12% cases did not show clear downward Poynting flux. The comparison between DMSP and Cluster data illustrates that the chance to observe large Poynting flux at high altitudes is smaller than at low altitudes, which indicates some heating processes existing between Cluster and DMSP satellite altitudes. Interestingly, 50 Cluster crossings (52%) had a certain period with significant upward Poynting flux in the cusp, which may be related to the configuration and dynamics of geomagnetic field in the high altitudes.
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