My daughter has a science project with the question, how does rainfall affect the ocean? Please help with a?

Answer 1

How do Raindrops Make Sound Underwater? Page 1Page 3


There are two components to the sound generated by a raindrop splash. These are the splat (impact) of the drop onto the water surface and then the subsequent formation of a bubble under water during the splash. The relative importance of these two components of sound depends on the raindrop size.


Surprisingly, for most raindrops, the bubble is by far the loudest source of sound. Bubbles are one of the most important components of underwater sound (Clay and Medwin 1977). They have two stages during their lifetimes: “screaming” infant bubbles and quiet adult bubbles. When a bubble is created, the pressure inside it is not at equilibrium with the pressure of the surrounding water. The water pushes against the bubble, compressing it. As the bubble shrinks, the air trapped inside increases in pressure. This occurs so rapidly that the pressure inside the bubble becomes higher than that of the water, so it expands to equalize, again overshooting. The bubble oscillates between high and low pressure at a high frequency, creating a distinctive and well-quantified sound. The sound radiates energy, so the bubble eventually reaches equilibrium with its surroundings.




The frequency of the sound is well defined (Minnaert 1993) and depends on bubble radius, local pressure, local water density, and a geophysical constant. The important observation is that the size of the bubble is inversely proportional to its resonance (ringing) frequency. Larger bubbles ring at lower frequencies and smaller bubbles ring at higher frequencies. The sound radiated is often loud and narrowly tuned in frequency (a pure tone). But quickly, after just tens of milliseconds, a bubble in water becomes a quiet adult bubble and changes its role—it absorbs sound and is especially efficient at absorbing sound at its resonance frequency.

Naturally occurring raindrops range in size from about 300 microns in diameter (a drizzle droplet) to more than 5 millimeters in diameter (often at the beginning of a heavy downpour). As the drop size changes, the shape of the splash changes and so does the subsequent sound production. In laboratory and field studies (Medwin et al. 1992; Nystuen 1996), scientists identified five acoustic raindrop sizes (see Table 1). For tiny drops (diameter less than 0.8 mm), the splash is gentle and no sound is detected. On the other hand, small raindrops (0.8—1.2 mm diameter) are remarkably loud. The impact component of their splash is still very quiet, but the geometry of the splash is such that a bubble is generated by every splash in a very predictable manner (Pumphrey et al. 1989). These bubbles are relatively uniform in size, and therefore frequency, and are very loud underwater. Small raindrops are present in almost all types of rainfall, including light drizzle, and are therefore responsible for the remarkably loud and unique underwater “sound of drizzle” heard between 13—25 kHz, the resonance frequency for these bubbles.
interestingly, the splash of the next larger raindrop size, medium (1.2-2.0 mm diameter), does not trap bubbles underwater and, consequently, medium raindrops are relatively quiet—much quieter than the small raindrops. The only acoustic signal from these drops is a weak impact sound spread over a wide frequency band. For large (2.0-3.5 mm diameter) and very large (greater than 3.5 mm) raindrops, the splash becomes energetic enough that a wide range of bubble sizes are trapped underwater during the splash, producing a loud sound that includes relatively low frequencies (1 - 10 kHz) from the larger bubbles. For very large raindrops, the splat of the impact is also very loud with the sound spread over a wide frequency range (1-50 kHz). Thus, each drop size produces sound underwater with unique spectral features that can be used to acoustically identify the presence of drops of a given size within the rain.

In order to measure rain at sea, scientists at the University of Washington’s Applied Physics Laboratory designed and built Acoustic Rain Gauges (ARGs). The ARG consists of a hydrophone (underwater microphone), some electronic circuitry, a low-power sampling computer, and a battery package designed to operate the ARG without servicing for up to a year. The ARG is attached to a mooring line, and can be placed at any depth in the ocean, although practically the depth is limited by the crushing strength of the instrument case. Every few minutes the ARG "wakes up" and evaluates and records the underwater sound field. Currently, the ARG design is autonomous from the surface float, and the recovery of data awaits recovery of the mooring. In the future, real-time transmission of the data will be needed to provide useful data for weather forecasting.

When listening for rain in the ocean, the first step is to identify the sound as rain. There are lots of other sounds underwater, including the sounds of waves breaking, man-made sounds and biological sounds. Biological and man-made sounds are sometimes very loud and, if they contain frequency components that overlap the rain-generated sound, then they can prevent acoustical measurement of rain. These noises are usually intermittent or geographically localized. Some locations where persistent "noise" is present includes harbors (shipping and industrial activity) and snapping shrimp colonies. Snapping shrimp are from a family of shrimp species that make very loud "snaps" and that inhabit shallow tropical waters. Fortunately, the frequency content of most sounds is unique to their sources, and can be used to identify the sources, including rain, drizzle, and whitecaps. Some examples of oceanic sound spectra are shown in the graph below.

Most of the time it is not raining and no man-made or biological noises are present. When this is true, the sound is from the whitecaps generated by wind and can be used to quantitatively measure wind speed (Vagle et al. 1990) as the number of whitecaps is proportional to wind speed. The shape of the sound spectrum generated by breaking waves is controlled by the distribution of bubble sizes generated by the breaking wave (Medwin and Beaky 1989). An interesting feature of the wind-generated signal is an apparent limit to the loudness of the sound at higher frequencies. This is due to quiet adult bubbles absorbing the higher frequency sound levels (Farmer and Lemon 1984). Because of their smaller size, bubbles that absorb high-frequency sound stay in the water longer and can form effective layers of sound-absorbing bubbles.



The graph at left shows examples of underwater sound spectra recorded from an oceanic mooring in the South China Sea. The sound spectra from wind-only conditions (green) show a uniform shape and a sound level which is proportional to wind speed. The sound of drizzle (light blue) shows the characteristic peak associated with the sound generation mechanism of the small raindrops. The sound of heavy rain (dark blue) is louder and includes lower frequencies. The sound of extreme rain includes sound generated by very large raindrops and is very loud. It also shows the effect of "quiet adult bubbles." Two spectra from extreme rain (200 mm/hr) are shown. The first (dark blue) shows extremely high sound levels at all frequencies. The second (burgundy) shows relatively lower sound levels above 10 kHz. This spectrum was recorded five minutes after the first, and yet the rainfall rate was still the same. A layer of bubbles had been injected into the sea surface. New "rain sound" has to pass through the bubble layer to reach the ARG sensor, and is partially absorbed by the bubbles. Since smaller bubbles (higher resonance frequency) are less buoyant than larger bubbles, they stay in the water longer and thus this bubble effect is most noticeable at higher frequencies. (Graph by Jeffrey A. Nystuen)
Using the graph above, the differences between wind-only and rain-generated spectra often appear to be subtle. However, by presenting the data in a different manner (below), acoustic identification of different weather conditions becomes apparent. The sound of rain and drizzle contains relatively more high frequency sound than the sound from wind-only conditions. Furthermore, rain is much louder. Even drizzle, under low wind speed conditions, has sound levels which can be orders of magnitude louder than wind-only conditions. The characteristic sound of drizzle, the 13-25 kHz peak, is sensitive to wind and has not been detected when the local wind speed is more than 8-10 m/s. On the other hand, the sound from heavy rain is very robust and can be detected even in very high wind speed conditions (over 20 m/s) (Nystuen and Farmer 1989). Extreme rain (over 100 mm/hr) is even louder, and can generate an ambient bubble layer that will distort the recorded sound spectrum.


I copy and paste these pages for you incase you can't get the website:http://earthobservatory.nasa.gov/Study/Rain/rain_3.html

Answer 2

Generally, a rainfall over the ocean will affect the salinity (salt content) of that region. Rainfall will also affect the ocean temperature. Rainfall on land will affect the ocean by creating run-off from land to sea. Rainfall will affect the inhabitants of the ocean by the same reasons, too. (Ocean water that is too salty, warm, dirty will drive marine life to live elsewhere, migrate, die, etc.)

Answer 3

See It Rust Sorry that's all I could think of! Heres another good one for next year or so Which One Pops The Top All you need to do is experiment with a bottle, some liquid, and some baking soda, which one launches the lid off with more force! its quite simple and a solid a!

Answer 4

it affects the ocean bcauz it is part of the water cycle, it changes the water in the ocean(i probably wrong though)

Answer 5

The rain fall increases the height of the tides... This is how they get the boats in water-side storage, so high up.

Answer 6

I think it would be about reducing the percent of salt in the ocean.

Answer 7

Libraries are chock full of information. Try there.

P.S. If you keep doing your daughter's homework, she will wind up learning nothing.

Answer 8

Let your daughter figure it out.