All nuclear detonations are air burst, usually at around 1,500 feet. Unlike a conventional demolition bomb witch has a detonator cap on the nose of the bomb a nuclear weapon has an electronically triggered detonation, a kind of ‘’shotgun’’ effect where the positive charged hydrogen atoms collide with the negative charged atoms and all hell breaks loose. You can’t have something that sophisticated and delicate smashing into the ground at around two hundred miles an hour.
You make a good point. However, the Hiroshima bomb was not that sophisticated. A TNT explosion slamming two masses of U-235 together. The real hard part was separating the 235 from the 238. Amazing that we were able to do that almost 80 years ago.
The flash is bright enough to blind, but doesn’t necessarily get caught on film because it is so brief. Mid-air detonation is done to maximize damage to the target — the Tunguska blast was a natural event, consisting of a circa 100-foot object blowing apart before ground impact, and trees were knocked down for miles. Right under the mid-air explosion a stand of trees was left, dead, with all their limbs and branches gone; a similar phenom directly under the blast at Hiroshima was called a “telegraph pole forest”.
Just to add the 1500 ft altitude is optimum for the most effective blast for those type of nukes. A burst lower than that would still be devastating but cause a crater and severely reduce the blast radius. A nuclear explosion at ground level would actually force much of the explosive power upward and be a waste.