Lightning

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globals [
  cloud-line      ;; y coordinate of bottom row of cloud
  surface        ;; y coordinate of top row of earth
  top-of-cloud
  bottom-of-cloud
  dust-probability
  fade-probability
  lightning-struck?
  hit-tree?
]

breed [trees my-tree]
breed [clouds cloud]
breed [positive-cloud-ions positive-cloud-ion]
breed [negative-cloud-ions negative-cloud-ion]
breed [positive-ground-ions positive-ground-ion]
breed [step-leaders step-leader]
breed [positive-streamers positive-streamer]


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;; Setup Procedures ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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;; ;;;;;; Setup ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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to setup
  clear-all
  setup-world
  reset-ticks
end 

;; ;;;;;; Setup World ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;; set up the world background
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to setup-world
  
  ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; set global variable values
  set cloud-line 100
  set surface -50; set the height of the earth
  set top-of-cloud 86
  set bottom-of-cloud (75 - (size-of-cloud))
  set dust-probability 70 ;; the probability the ionzation will happen to a dust particle
  set fade-probability 1 ;; the probability a path of ionized air will end or fade
  set lightning-struck? false
  set hit-tree? false
  
  ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; set colors for the patches in the background
  ask patches [
    if pycor = surface ;; set color of the earth surface with input number of positive streamers
      [set pcolor green - 1] 
    if pycor > (cloud-line - 1)
      [set pcolor gray]    ;;set color of the cloud
    if pycor > surface and pycor < cloud-line
      [set pcolor black]  ;; set color of the sky 
    if pycor < surface 
      [set pcolor green] ;; set color of the earth
  ]
  
  ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; create the trees in the meadow based on the slider value for the number of trees
  create-trees number-of-trees [
    ;; half the trees are trees and half are pines
    ifelse ((random 2) = 0) 
    [set shape "myTree"]
    [set shape "myPineTree"]
    set size ((random 20) + 15)  
    setxy random-pxcor (surface + size / 2) 
  ]
  
  ;;create cloud
  create-clouds 1 [
    set shape "cloud"
    set size (size-of-cloud * 20)
    setxy 0 75
  ]
  
  ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;create Ions in the world and cloud
  create-positive-cloud-ions strength-of-field
  create-negative-cloud-ions strength-of-field
  create-positive-ground-ions strength-of-field
  
  ask positive-cloud-ions [
    set shape "+"
    set size 7
    setxy random-x-in-cloud (top-of-cloud - random-y-in-cloud)
  ]
  
  ask negative-cloud-ions [
    set shape "-"
    set size 7
    setxy random-x-in-cloud (bottom-of-cloud - random-y-in-cloud) 
  ]  
  
  ask positive-ground-ions [
    set shape "+"
    set size 7
    setxy random-x-in-cloud (surface - random 15) ;; distribute randomly along the surface, beneath the cloud area
  ]
  
  setup-streamers-leaders
  add-dust 
end 

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;;create and place the streamers and leaders
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to setup-streamers-leaders
  
  ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;create lightning makers
  create-step-leaders strength-of-field  
  ask step-leaders [
    set shape "negativeStrm"
    set size 5
    let xcoor ((random (size-of-cloud * 15)) - (size-of-cloud * 7))
    setxy xcoor (bottom-of-cloud - (size-of-cloud * 2))
    facexy xcoor surface
  ]
  
  create-positive-streamers strength-of-field
  ask positive-streamers [
    set shape "positiveStrm"
    set size 5
    let xcoor random-x-in-cloud
    setxy xcoor surface
    while [(pcolor = lime) or (pcolor = turquoise) or (pcolor = brown)] [
      set ycor (ycor + 1) 
    ]
    facexy xcoor bottom-of-cloud
  ]
end 

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;; The ions move around as a result of bouncing around and colliding (not explicitly modelled).
;; There is a charge separation within the cloud, the cause of which is not entirely understood,
;; although there are theories.  The separation is illustrated in this model, but the underlying
;; cause/process of the separation is not explicitly modelled.
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to make-ions-move
  ask positive-cloud-ions [ ;; set the position to a random X, and change the Y by a random amount to stay in upper area of cloud
    setxy random-x-in-cloud (top-of-cloud - random-y-in-cloud)
  ]
  ask negative-cloud-ions [;; set the position to a random X, and change the Y by a random amount to stay in lower area of cloud
    setxy random-x-in-cloud (bottom-of-cloud - random-y-in-cloud) 
  ]
end 

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;;; determine the area of the cloud
;;; and randomly select positions from width and height (X and Y)
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;; get a random X coordinate within the cloud's area

to-report random-x-in-cloud
  ;; the width is determined by multiplying the size-of-cloud variable by 15
  ;; however, we subtract a multiple of the size to make the distribution cover the positive and negative regions of the axis 
  report random (size-of-cloud * 15) - (size-of-cloud * 7)
end   

;; get a random Y coordinate within the cloud's area

to-report random-y-in-cloud
  ;; the height of the cloud is determined by doubling the size-of-cloud variable
  report random (size-of-cloud * 2)
end 

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;;; disperse dust into the air
;;; these particles influence the path of the lightning
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to add-dust
  ask n-of dust patches with [pycor > surface  and pycor < cloud-line] [
    set pcolor gray - 2
  ]
end 

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;;; Runtime Procedures ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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to go 
  ;; if lightning has struck, clear the faded paths as the charge has now been neutralized 
  if lightning-struck? [
    clear-fades ;; if there's been a lightning strike, clear all the faded paths
    stop  
  ]
  
  ;; if the leaders and streamers have all died or faded, stop the model
  if (not any? step-leaders) and (not any? positive-streamers) [
    stop
  ]
  
  ;; since the positive streamers grow at a slower rate than the step leaders,
  ;; we keep track of the time so make them move at appropriate times compared to each other
  
  ;; the step leaders leave the cloud and move towards the earth at one patch per tick
  move-step-leaders-down
  
  ;; meanwhile, the positive streamers extend from the earth towards the cloud, but at a slower rate
  if ticks > 50
    [grow-positive-streamers-up]
  
  ;; as time moves on the ions move around the cloud
  make-ions-move
  
  tick 
end 

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;; get the step leaders to move towards the earth
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to move-step-leaders-down
  let movex 0
  let movey 0
  
  ask step-leaders[
    set moveX 1000 ;; default values to indicate that the move coordinates have not been set
    set moveY 1000
    
    ask neighbors with [pcolor = gray - 2] [ ;; if the patch is gray then the leader 
                                             ;; has reached a dust particle and is more likely 
                                             ;; move that direction and ionize it
      if random 100 < dust-probability [
        set movex pxcor
        set movey pycor
      ]
    ]
    
    ;; if the stepleaders sense a positive streamer they move towards it
    let xcoor xcor
    let ycoor ycor
    
    ;; so we check for positive streamers between the leader and the ground
    ask patches in-cone 10 60 [
      
      ifelse any? trees-here ;; if any tree exists in the local area
      [
        ifelse ((xcoor - pxcor) > 0)   ;; check if it is to the left
          [set movex (xcoor - 1)] ;; then move one step to the left
          [set movex (xcoor + 1)] ;; otherwise, it is to the right, so move one step to the right
        
        set movey (ycoor - 1) ;; move down one step closer to the surface
      ]         
      [
        if any? positive-streamers-here ;; if one exists then the leader moves in the direction towards it
          [ ifelse ((xcoor - pxcor) > 0)   ;; if the positive streamer is to the left
            [set movex (xcoor - 1)] ;; then move one step to the left
            [set movex (xcoor + 1)] ;; otherwise, it is to the right, so move one step to the right
          
          set movey (ycoor - 1) ] ;; move down one step closer to the surface
      ]]
    
    ;; if no charges or dust particles are encouraging direction, pick at random but most likely toward earth
    ;; the random numbers are used to show the probabilities of ionized air moving in specific directions. 
    ;; the path will move based on some probability of ten by selecting a random number below 10.
    ;; these probabilities are not scientific and are used only to help guide the path
    
    if movex = 1000 [
      
      ;;set y movement
      let rand-no random 10
      
      ;; if that number is greater than 2, the path will move directly down one towards earth (80%). 
      ;; if it is less than 2 the path won't move (10%)
      ;; if it is 2 the path will move up one towards the cloud (10%)
      
      ifelse (rand-no > 2)[
        set movey ycor - 1
      ][
      ifelse (rand-no < 2)[
        set movey ycor
      ][
      set movey ycor + 1
      ]
      ]
      
      ;; if that number is greater than 6, the path will move to the left (40%). 
      ;; if it is less than 2 the path won't move (20%)
      ;; if it is between 2 and 5 the path will move to the right (40%)
      
      ;;set x movement
      set rand-no random 10
      
      ifelse (rand-no > 6)[
        set movex xcor - 1
      ][
      ifelse (rand-no < 3)[
        set movex xcor
      ][
      set movex xcor + 1
      ]
      ]     
    ]
    
    ;; make sure its still in the bounds of the world; otherwise, the path fades
    ifelse (movex < min-pxcor) or (movex > max-pxcor) or (movey > max-pycor)
      [die]
      [If (random 100 < fade-probability) ;; these is some chance (the fade-probability) that the path will fade on its own
        [die]   
      setxy movex movey
      ]
    
    ;; check if the path hit a tree
    did-hit-tree
    
    ;; and change whatever patch the leader has moved to plasma, or a blue patch
    ask patch-here [
      ifelse (any? positive-streamers-here or  ;; if that patch is a positive streamer, or
        (pcolor = (violet + 3)) or               ;; the path of a streamer, or
        (hit-tree?) or                         ;; a tree, or
        (pycor = surface))                       ;; the earth's surface  
      [ make-lightning movex movey                     ;; then lightning strikes and we turn the patch yellow
        set pcolor yellow ]
      [ set pcolor (blue + 3)]                     ;; otherwise, turn that patch of air to plasma (ie, a blue patch)
    ]
  ] 
end 


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;; here we approximate the position of trees using a circle roughly the size of the trees
;; if the step leader path reaches the tree, lightning strikes
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to did-hit-tree
  ask patches in-radius 12 [
    if any? trees-here 
      [ set hit-tree? true ]
  ]
end 

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;; grow the positive streamers toward the cloud
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to grow-positive-streamers-up
  
  ask positive-streamers [
    let movex 0
    let movey 0
    
    ;;;;;;;;;;;;;;;;;;; if the patch is gray then the leader has reached a dust particle and is more likely to ionize it
    ask neighbors [
      if pcolor = gray - 2 [ 
        if random 100 < dust-probability [
          set movex pxcor
          set movey pycor
        ]
      ]
    ]
    
    ;;;;;;;;;;;;;;;;; generate random direction moves for the path to grow
    if (movex = 0)[    
      ;;set y movement
      let rand-no random 10
      
      ifelse (rand-no < 8)[
        set movey ycor + 1
      ][
      ifelse (rand-no < 2)[
        set movey ycor
      ][
      set movey ycor - 1
      ]
      ]
      
      ;;set x movement
      set rand-no random 11       
      ifelse (rand-no < 5)[
        set movex xcor - 1
      ][
      ifelse (rand-no < 2)[
        set movex xcor
      ][
      set movex xcor + 1
      ]
      ]     
    ]
    
    ;;;;;;;;;;;;;;;;; if the movement is off the screen, kill the stream    
    let random-growth-height (surface + random 20 + 20)
    
    ifelse (moveX < min-pxcor) or (movex > max-pxcor) or 
      (moveY < surface) or (movey > max-pycor) or
      (moveY > random-growth-height)
      [die]
      [if (random 100 < fade-probability)  ;;there is some probability that the stream will just end 
        [die]   
      setxy movex movey
      ]
    
    ;;;;;;;;;;;;;;;;; if the patch is empty then change the color to show the path is now positive
    ;;;;;;;;;;;;;;;;; if the patch has both a stepleader and a positive streamer the paths connect and lightning strikes!
    ask patch-here [
      ifelse (any? step-leaders-here or (pcolor = (blue + 3)))
        [make-lightning movex movey
          set pcolor yellow ]
        [set pcolor (violet + 3)]
    ]
    
  ] ;; end ask +streamers
end 

;;; ;;;;;;; Make Lightning ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;; we'll check all the neighboring patches to see if they've been ionized (or turned light blue color)
;; if they have been they are now charged and send it to their neighbors as well
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to make-lightning [x y]
  set lightning-struck? true
  create-strike x y
end 

to create-strike [x y]
  if (y < bottom-of-cloud) and (y > (surface - 1)) [
    ask neighbors [
      if (pcolor = (violet + 3)) or (pcolor = (blue + 3)) [  
        set pcolor yellow
        make-lightning pxcor pycor
      ]
      if pcolor = black [
        set pcolor white
      ]
    ]
  ]
end 


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;;clear the remaining positive streamers from the sky
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to clear-fades  
  ask patches [
    if (pcolor = (violet + 3)) or (pcolor = (blue + 3)) [
      set pcolor black
    ]
  ]
  ask positive-streamers [ die ]
  ask step-leaders [ die ]
end 


; Copyright 2011 Uri Wilensky.
; See Info tab for full copyright and license.