When we think of rainbows, we often envision them arcing across the sky after a rain shower. However, there is another type of rainbow that occurs closer to the Earth's surface - the sea water rainbow. This captivating atmospheric optics phenomenon occurs when light interacts with sea spray, creating a beautiful display of colors. In this article, we will delve into the intricacies of sea water rainbows and explore why they differ from their sky-high counterparts.
The most noticeable distinction between sky rainbows and sea water rainbows is their position. While sky rainbows appear above the horizon, sea water rainbows are situated below it. This difference in location arises from the distinct mechanisms that give rise to each type of rainbow.
Sky rainbows are formed by sunlight refracting and reflecting within raindrops in the atmosphere. On the other hand, sea water rainbows are created by the interaction of light with tiny water droplets present in sea spray. These droplets are generated when waves crash against the surface of the ocean, propelling small particles of water into the air.
One striking characteristic of sea water rainbows is their slightly smaller radius compared to sky rainbows. This variation in size arises from the difference in the refractive properties of saltwater and rainwater. Saltwater, being denser and containing dissolved salts, refracts light more strongly than rainwater. As a result, the sea water rainbow appears approximately 0.8 degrees smaller in radius.
Interestingly, materials that refract light even more strongly than saltwater can produce even smaller rainbows. For instance, glass has a refractive index higher than that of rainwater, leading to the formation of bows that are approximately half the size of rainwater bows.
Photographers and nature enthusiasts have been captivated by the ethereal beauty of sea water rainbows. These mesmerizing displays can often be observed in coastal areas, where the interaction between waves and the shoreline creates an abundance of sea spray. Photographers have successfully captured the vibrant colors and delicate arcs of sea water rainbows, showcasing the unique charm they bring to the natural world.
The world of atmospheric optics never ceases to amaze us, and sea water rainbows serve as a testament to the wondrous interplay between light and nature. While sky rainbows may be more commonly observed, the enchanting allure of sea water rainbows provides a captivating spectacle for those fortunate enough to witness them. So, the next time you find yourself near the ocean on a sunny day, keep an eye out for these lesser-known rainbows dancing below the horizon.
Sea Water Bow
The bow below the horizon does not match the one in the sky.
The upper bow is an ordinary bow made by falling rain.
The lower bow was formed by sea spray.
The sea water bow has a slightly smaller (by ~0.8°) radius because salty water refracts light more strongly than rainwater.
Materials that refract light even more strongly produce smaller bows still. Glass makes bows about half the size of rainwater bows.
Photographed in the Pacific Ocean by J Dijkema.
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"Sea Water Rainbow". Atmospheric Optics. Accessed on December 10, 2023. https://atoptics.co.uk/blog/sea-water-rainbow/.
"Sea Water Rainbow". Atmospheric Optics, https://atoptics.co.uk/blog/sea-water-rainbow/. Accessed 10 December, 2023
Sea Water Rainbow. Atmospheric Optics. Retrieved from https://atoptics.co.uk/blog/sea-water-rainbow/.