Investigating into natural lighting

Lighting accompanies thunderstorms, during which large amounts of energy are released without being leased. Despite the ostensible familiarity, lighting is still enigmatic, as described in this interview:

We learn about lightning in school, I thought it was a closed case?
Well, we know lightning initiates up inside a thunderstorm but we're not sure how it initiates – how it gets started. In fact there are still three big questions. The first is the initiation. The second is how does it propagate, sometimes through miles of air? And the third is, when it reaches the ground – how does it choose to strike this object and not the other object?

But isn't it just an electrical discharge between thunderclouds and the ground?
In a sense, but the big problem is that to get a spark, air needs to break down. It needs to stop being an insulator and start being a conductor. We commonly experience this if you touch a doorknob and you get a spark between your finger and the doorknob. What happens is the charges get concentrated into your fingertip and you get a big electric field. Then, as your finger approaches, the conventional breakdown field is reached, which is about 3 million volts per metre – and then air sparks.

The problem is if you look up inside thunderclouds, the breakdown field that you need to make a spark is never found. People have been launching balloons for decades, they've been flying airplanes, they've been launching rockets...but the fields they record are not even close to this strength.