製作太陽全時影像以研究日冕洞隨時間的變化;Constructing Solar Synoptic Maps to Study The Temporal Variations of Coronal Holes

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Title:	製作太陽全時影像以研究日冕洞隨時間的變化;Constructing Solar Synoptic Maps to Study The Temporal Variations of Coronal Holes
Authors:	黃冠瀚;Huang,Guan-Han
Contributors:	太空科學研究所
Keywords:	全時影像;日冕洞;高速太陽風;卡靈頓座標;synoptic map;coronal hole;high-speed stream;Carrington coordinates
Date:	2016-01-20
Issue Date:	2016-03-17 18:47:28 (UTC+8)
Publisher:	國立中央大學
Abstract:	全時影像（synoptic map）是用於近似全表面太陽的影像。我們使用CR2099至CR2158期間，Solar Dynamics Observatory的Atmospheric Imaging Assembly與Helioseismic and Magnetic Imager的資料製作全時影像，以研究極紫外線影像中的暗區，日冕洞。每一張全時影像由48幅中央經線太陽影像所構成，並且按照時間順序排列。全時影像經由臨界值法找出全時影像中的低亮度區域。若一低亮度區域的磁場偏度（skewness）超過0.35，則該區域被判斷為日冕洞。我們將太陽分為北極區（65°至90°）、中低緯區（-65°至65°）以及南極區（-90°至-65°），討論日冕洞面積、磁通量絕對值的變化。結果顯示中低緯區日冕洞占了中低緯區約5%的面積，磁通量絕對值約為0.8×10^22 Mx；南極區日冕洞占了南極區約30%的面積，磁通量絕對值約為0.4×10^22 Mx。因為南極區明顯比中低緯區小，顯示磁場於南極區日冕洞比起中低緯區日冕洞要強。此外我們結合了Advanced Composition Explorer的Real-Time Solar Wind觀測資料，嘗試由1 AU處追蹤高速太陽風粒子至太陽表面。結果顯示48%的高速太陽風來源接近日冕洞的中心。;Synoptic maps are approximations of the full surface of the sun. We construct synoptic maps from CR2099 to CR2158 to study the dark regions on the EUV image called coronal holes. The data are retrieved from Atmospheric Imaging Assembly and Helioseismic and Magnetic Imager onboard Solar Dynamics Obervatory. Each synoptic map contains 48 central meridian images arranged in time series. Dark regions are extracted by the thresholding routines. A dark region is identified as a coronal hole if its magnetic field skewness exceeds 0.35. The sun is divided into north-polar (65° to 90°), mid-low latitude (-65° to 65°) and south-polar (-90° to -65°) region. Each region the area and unsigned flux of coronal holes are calculated and discussed. The result shows that mid-low latitude holes occupy 5% the area of mid-low latitude region, with unsigned flux 0.8×10^22 Mx. South-polar holes occupy 30% the area of the south polar region, with unsigned flux 0.4×10^22 Mx. Since south-polar region is much smaller than the mid-low latitude region, the magnetic field is stronger in south-polar holes than in mid-low latitude holes. In addition, we combine synoptic maps with Real-Time Solar Wind measurements on Advanced Composition Explorer, and try to trace fast solar wind particles from 1 AU back to the solar surface. The result shows that 48% of fast solar wind sources are close to the center of coronal holes.
Appears in Collections:	[Graduate Institute of Space Science] Department of Earth Sciences

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