SADs typically begin 100–200 Mm above the photosphere and descend 20–50 Mm before dissipating near the top of the flare arcade after a few minutes. Sunward speeds generally fall between 50 and 500 km s but may occasionally approach 1000 km s. As they fall, the downflows decelerate at rates of 0.1 to 2 km s. SADs appear dark because they are considerably less dense than the surrounding plasma, while their temperatures (100,000 to 10,000,000 K) do not differ significantly from their surroundings. Their cross-sectional areas range from a few million to 70 million km (for comparison, the cross-sectional area of the Moon is 9.5 million km).