Key points
Prior knowledge: Low-magnetic-latitude Very Low Frequency radio transmission in the Earth-Ionosphere Waveguide is suppressed for propagation toward magnetic West, relative to magnetic East.
New finding: This magnetic-westward suppression is dramatically stronger during night than during day.
New finding: The magnetic-westward suppression at night applies to nearly the entire westward half-plane, from magnetic-South clockwise to magnetic-North.
New finding: The magnetic-westward suppression at night is readily observable for dip angles in the range -30 deg to +30 deg.
Index terms: 2487, 6934, 6964,