Static positive charge of thunder cloud(high positive voltage(KV)), produced by high velocity wind, discharge to ground through lightening, following zig zeg (step by step ionization of air to reach ground) path in air, and is HVDC, called direct stroke, when two charge cloud come close the total raised charged produced lightening called indirect stroke, same positive charge of both also produced loud sound with repulsive vibrating energy wave, called thunder and as, velocity of light is higher than sound we see lightening before the sound and vibration waves.

This is static charge transfer from cloud to ground. In the meanwhile that include varying  current but can't be say AC or DC because for the single return stroke it would transfer the single charge. But in same path it can be many return stroke and much changes in the sign. In every time the frequency can be vary from VLF to VHF due to random nature of this phenomena. That is variable quantity. 

Current in lightning channel during the single stroke is the direct one by charges' movement direction. A magnitude of lightning current increases very fast in the beginning period lasted 1-1.5 microseconds and then undergoes dropping during a few dozens microseconds. 

Hi  Mahamad Nabab Alam

The current at the channel base is  a function of height and time. The discharging process is separated into (1) the exponential discharge of the leader head and leader core with a relatively short time constant, less than 1µs, which we call the ”breakdown” time constant, and (2) the exponential discharge of the charge stored around the leader core with a longer time constant, of the order of microseconds.

Many functions were considered for simulating the lightning return-stroke current (Heidler’s pulse models, Analytical expression of ; Diendorfer- Uman,  Nucci Cooray, ...etc.). You can't say AC or DC current because the lightning current has been studied as a pulse waveform. The double exponential expression is adopted to simulate this current. This pulse, have only been created for design purposes, happens to be very simple to treat of pulse amplitude, rise time and pulse duration can be easily studied. The time expression can be characterized as: i(t) = I_max (exp(−at) − exp(−bt))

Good luck,

Omar

Algeria

This can only be understood by putting the planet Earth into its larger electrical environment. Lightning on Earth, Jupiter, and Saturn is shown to be correlated with the solar wind.