Lived in Bay Area for 11 years. Loved it and hated it, beautiful place. That blue hue is from the exhaust particles being exited and passing through the Van Allen Belt in the outer atmosphere. After engine burn, the particles will remain excited, leaving the blue trail. We normally conducted these out in the north Pacific where no one would see them, as do the Russians (Soviets when I was up there). We would shadow their monitor ships along with the Observation Island. Good times. This was obviously done for maximum viewing, reassurance and to send a message.