what type of air tends to sink
Cold air is denser and heavier than warm air, so it tends to sink while warm air tends to rise. In areas where winds converge at high altitude, cold air sinks and creates a temporary buildup of air near the Earth's surface and thus a zone of high pressure. Atmospheric pressure decreases with increasing altitude, so high pressure is actually a relative term; generally, weather forecasters use this to mean high relative to normal atmospheric pressure at that altitude.