In photography this is called Rim Lighting, because only the edge of the object has direct light. To do it right you need an extra person or two holding some big ass reflectors to fill in the shadows. You captured the effect quite nicely.
A few pointers. Only one side can be rim lit by the sun (in the studio, you can do just about anything...). So the 'main' light would be, say, to the top left. So any edge on the bottom or right side (of the picture) would not have as strong of a highlight. In this case, there would be a weaker and more diffuse light reflecting off the sand or water.
When I draw, and I admit I'm terrible at it, I actually draw a little arrow to indicate the direction of the main light. This a habit I got into when designing lighting for a photograph, back when I had lots of studio equipment... I still find it helpful.