The code

/*
Programming for Artists - Assignment #8
Brock J. Stearn
"Rain"
*/
// Wave formula:
// wavelength = amplitude * periodicFunction(frequency * time + phaseShift)
// (From Pete) define a function to perform updates to the stage
function circleAnimationstep(whichCircle, bounds) {
	// (From Pete) bounds[0] = left edge of cell
	// (From Pete) bounds[1] = top edge of cell
	// (From Pete) bounds[2] = right edge of cell
	// (From Pete) bounds[3] = bottom edge of cell
	var period = 7*1000;
	var milliseconds = (new Date()).getTime();
	var radians = (2*Math.PI)*((milliseconds%period)/period);
	var norm = whichCircle/circles.length;
	var frequency = 2;
	var phaseShift = norm*(2*Math.PI);
	var ranOpac = Math.random()*100;
	var rany = Math.random()*10;
	// Use implemented Square and Saw functions to create Rain look
	if (rany <= 2) {
		// Saw gives a wave like effect
		circles[whichCircle]._x = rangedSaw(radians, frequency, phaseShift, bounds[0], bounds[2]);
	} 
	else {
		// Square creates more straight drops
		circles[whichCircle]._x = rangedSquare(radians, frequency, phaseShift, bounds[0], bounds[2]);
	}
	circles[whichCircle]._y = rangedSaw(radians, frequency, phaseShift, bounds[3], bounds[1]);
	// Add some alpha to create a misty fog like effect
	circles[whichCircle]._alpha = ranOpac;
	if (circles[whichCircle]._y < 350) {
		// Make raindrops ... x of 50 and y of 100 (no scale)
		circles[whichCircle]._xscale = 50;
		circles[whichCircle]._yscale = 100;
	} else {
		// Make Splash ... x of 200 and y of 50
		// Lower y value made the blue disappear ... looked too much like shadows
		circles[whichCircle]._xscale = 200;
		circles[whichCircle]._yscale = 50;
		// Make puddles lighter
		circles[whichCircle]._alpha = ranOpac*.5;
	}
}
//
//----------------------------------------------------------------------------------
// constants:
var numCols = 5;
var numRows = 5;
var col = Stage.width/numCols;
var row = Stage.height/numRows;
// Array of all circle objects (movies)
var circles = new Array(circle01, circle02, circle03, circle04, circle05, 
						circle06, circle07, circle08, circle09, circle10, 
						circle11, circle12, circle13, circle14, circle15, 
						circle16, circle17, circle18, circle19, circle20, 
						circle21, circle22, circle23, circle24, circle25);
// (from Pete)
function updateFrame() {
	var curRow = 0;
	var curCol = 0;
	for (var j = 0; j < circles.length; j++) {
		var lo_x = (col*curCol)+(.5*circles[j]._width);
		var hi_x = (col*(curCol+1))-(.5*circles[j]._width);
		var lo_y = (row*curRow)+(.5*circles[j]._height);
		var hi_y = (row*(curRow+1))-(.5*circles[j]._height);
		//
		curCol++;
		if (curCol == numCols) {
			curRow++;
			curCol = 0;
		}
		//
		circleAnimationstep(j, new Array(lo_x, hi_y, hi_x, lo_y));
	}
}
// (from Pete) - Range Sine function
function rangedSin(t, f, p, lo, hi) {
	var a = (hi-lo)*.5;
	var mid = lo+a;
	return mid+(a*Math.sin(f*t+p));
}
// (from Pete) - Range Cosine function
function rangedCos(t, f, p, lo, hi) {
	var a = (hi-lo)*.5;
	var mid = lo+a;
	return mid+(a*Math.cos(f*t+p));
}
// ------ My Helpers ------ 
// Sawtooth
function sawtoothWave(value) {
	// t should be a fractional number > 0
	// period is 2
	// output is [-1,1]
	return ((value%1.0)*2)-1.0;
}
// SquareWave
function squareWave(value) {
	// t should be a fractional number > 0
	// period is 2
	// output is [-1,1]
	var v = -1;
	if (value%1.0>=.5) {
		v = 1;
	}
	return v;
}
// Range the Saw Function from above
function rangedSaw(t, f, p, lo, hi) {
	// t = time (varying value, should range [0,2PI])
	// f = frequency (waves per time, >= 1.0)
	// p = phase shift (affects timing of wave, should range [0,2PI])
	// lo = lower bound of arbitrary range
	// hi = upper bound of arbitrary range
	var a = (hi-lo)*.5;
	var mid = lo+a;
	return mid+(a*sawtoothWave(f*t+p));
}
// Range the Square Function from above
function rangedSquare(t, f, p, lo, hi) {
	// t = time (varying value, should range [0,2PI])
	// f = frequency (waves per time, >= 1.0)
	// p = phase shift (affects timing of wave, should range [0,2PI])
	// lo = lower bound of arbitrary range
	// hi = upper bound of arbitrary range
	var a = (hi-lo)*.5;
	var mid = lo+a;
	return mid+(a*squareWave(f*t+p));
}
//
//
// associate a function with the enterFrame event
this.onEnterFrame = updateFrame;