The most difficult hy­drol­o­gy riddles

This instability can occur, when there is velocity shear in a single continuous fluid, or where there is a velocity difference across the interface between two fluids. An example is wind blowing over water: The instability manifests in waves on the water surface. More generally, clouds, the ocean, Saturn's bands, Jupiter's Red Spot, and the sun's corona show this instability.

A hydrophone is a microphone designed to be used underwater for recording or listening to underwater sound.A hydrophone can detect airborne sounds, but will be insensitive because it is designed to match the acoustic impedance of water, a denser fluid than air. Sound travels 4.3 times faster in water than in air, and a sound wave in water exerts a pressure 60 times that exerted by a wave of the same amplitude in air.

IMarine snow refers to organic particulate matter that constantly falls from the upper waters into the deeper waters of the ocean. Marine snow serves to provide food and energy from the productive upper waters exposed to sunlight to the marine organisms that reside in the deeper regions of the water column. The content and abundance of marine snow varies seasonally and with variations in ocean currents.

Two large circular currents, one in the northern hemisphere flowing clockwise and one south of the equator moving anticlockwise, constitute the dominant flow pattern. During the winter monsoon, however, currents in the north are reversed