Lightning is so very interesting!!!
The Elect. Engineering Manuals Sittin' Up On My Shelves - Collecting Dust
each have an entire section devoted to "What Is Thought To Be Correct - So Far" regarding the phenomena.
Stroke Leaders "Pop" out from both sides - downwards from highly negative charged Cloud formations, and upwards from Earth bound areas of high Positive charge concentrations.
The Earth bound surface areas directly below the Cloud mass become Positively Charged, due to the increasing Negative Charge levels "Pressed Against" the Earth areas, from the Cloud mass above.
Negative charges in the ground areas are repelled away, leaving Positive charged moles O' dirt (and attracting additional Positive charge carriers).
All this increases until the dielectric strength of the enviromental Air gets punctured - then at least two stroke leaders connect, resulting in a discharge path.
The connection brings in an initiating arc, then the Plasma is developed. The Plasma is commonly oriented in an increasing "Step" from Ground to Cloud (appears to begin at the ground and "run up to the cloud"), whereas the initiating arc pulses downwards from the cloud.
The arc comes first, then the Plasma is created - which "Pushes" against the surrounding Air as it increases in size, and consequently as it decreases in size, the Air rushes into the void space.
That's where the thunder comes from!
If you are in the field of influence prior to a discharge event, you will feel its Capacitive field effects (hair will stand on ends).
That is the time for you to hit the floor!!!
To sum things up:
Water "cracking" into Ice when it freezes, generates the abundant Electrical Energy
(actually there are some other factors - even discharges from ABOVE
the Stratosphere Clouds shooting downwards to the cloud mass, but too much to cover!).
The Charges in Cloud masses become oriented with Negative ones towards the bottom of clouds, and + towards the top.
Charges increase as more Ice cracks from Liquid Water (the water loses a small mass when becoming solid - hence the resulting energy "output").
As charges increase in the clouds, the ground plane becomes the "Opposite Plate" of the "Capacitor" and has a resultant "+" charge.
As the charge levels become high (+2 to +5 KV / Meter), "Stroke Leaders" begin to "Reach" towards the opposite polarity (up from ground, down from cloud). The entire event is similar to a Capacitor - with the cloud base being the "-" abundant plate, the Earth being the "+" abundant plate, and the surrounding air being the "Dielectric" between the plates.
When the field strength / charge level, develope to a point which results in a potential difference of +15 KV / Meter, stroke leaders are long enough to make connections.
Many leaders connect, but the ones of best conduction result in the visible event blasts.
At the point(s) of highest conduction, the initializing arc "Smacks Together" via the leaders - tearing the dielectric strength at that location.
This is usually heard as a "Loud Hard Clap" followed with a "Ripping" like sound.
The rip sounds like it is coming down from the clouds.
After the arc is setup, the Plasma begins its "Pulses" against the surrounding air.
The Plasma pulses rise in strength, become somewhat stable as the charges begin to flow easilly, then as the clouds' charges decay, the pulses lose strength and eventually cease all together - marking the end of that complete event.
Plasma pulses may range from as little as 10, upto hundreds per an event.
As the Plasma flows, it makes a more conductive path, so more charges flow.
As more charges flow, the Plasma becomes more conductive path, so it increases in size.
The Plasma pulses outwards in strength against the surrounding air - which keeps it "In Check", and has an energy transfer involve (compressing the air requires energy - and the resultant sound generated - the Thunder, also requires energy).
When the energy state become "Neutral" (or at least close to it), the event is complete.
The entire process repeats as needed per imbalanced energy levels are developed.
Sorry to throw in such simple and quick & dirty descriptions here.
Also, my descriptions are somewhat "odd", likely due to it being years since I've discussed this stuff!
There's TONS more to study in this area of theory, so have fun!