Which ionospheric region is closest to the surface of Earth?
The correct answer is A: The D region. The ionospheric region closest to the surface of Earth is the D region. D region is the lowest ionospheric layer, typically 50-90 km above Earth's surface. For amateur radio operators, D region primarily absorbs signals rather than reflecting them. Understanding this helps explain ionospheric structure.
Exam Tip
Closest ionospheric region = D region. Think 'D' region = 'D'own (closest to Earth). D region is lowest ionospheric layer (50-90 km), closest to Earth's surface. E, F1, and F2 are progressively higher.
Memory Aid
"Closest ionospheric region = D region. Think 'D' region = 'D'own (closest). D region is lowest ionospheric layer (50-90 km), closest to Earth's surface. Primarily absorbs signals. E, F1, F2 are progressively higher."
Real-World Application
The ionospheric regions are layered: D region (50-90 km, closest to Earth, primarily absorbs), E region (90-150 km, reflects), F1 region (150-250 km, reflects), and F2 region (250-400 km, highest, reflects). D region is the closest to Earth's surface.
Key Concepts
Why Other Options Are Wrong
Option B (E region): Incorrect. E region is higher than D region - E is typically 90-150 km, while D is 50-90 km. D is closer to Earth.
Option C (F1 region): Incorrect. F1 region is much higher - F1 is typically 150-250 km, much higher than D region.
Option D (F2 region): Incorrect. F2 region is the highest - F2 is typically 250-400 km, much higher than D region.
题目解析
The correct answer is A: The D region. The ionospheric region closest to the surface of Earth is the D region. D region is the lowest ionospheric layer, typically 50-90 km above Earth's surface. For amateur radio operators, D region primarily absorbs signals rather than reflecting them. Understanding this helps explain ionospheric structure.
考试技巧
Closest ionospheric region = D region. Think 'D' region = 'D'own (closest to Earth). D region is lowest ionospheric layer (50-90 km), closest to Earth's surface. E, F1, and F2 are progressively higher.
记忆口诀
Closest ionospheric region = D region. Think 'D' region = 'D'own (closest). D region is lowest ionospheric layer (50-90 km), closest to Earth's surface. Primarily absorbs signals. E, F1, F2 are progressively higher.
实际应用示例
The ionospheric regions are layered: D region (50-90 km, closest to Earth, primarily absorbs), E region (90-150 km, reflects), F1 region (150-250 km, reflects), and F2 region (250-400 km, highest, reflects). D region is the closest to Earth's surface.
错误选项分析
Option B (E region): Incorrect. E region is higher than D region - E is typically 90-150 km, while D is 50-90 km. D is closer to Earth. Option C (F1 region): Incorrect. F1 region is much higher - F1 is typically 150-250 km, much higher than D region. Option D (F2 region): Incorrect. F2 region is the highest - F2 is typically 250-400 km, much higher than D region.
知识点
D region, Ionospheric regions, Closest to Earth, Ionospheric structure
Verified Content
Question from official FCC General Class question pool. Explanation reviewed by licensed amateur radio operators.