[Corli de Kock]

Corli de Kock asked the Naked Scientists:

We have been wondering for quite a while why the ocean seems louder at night than during the day?

Is it because of the "masking" phenomenon or because of a possible effect that temperature fluctuation has on the air and subsequently on the speed of sound?

My mom's a great fan of your segment on 702 here in South Africa, so she suggested I ask you...

Hope you'll be able to help!

What do you think?

[RD]

At night it is cooler than in the day.
The extent to which air bends sound waves (refactive index) is inversely proportional to temperature.

At night, because the air is cooler, more of the sea sounds are directed (bent) towards the land because the refactive index of the air has increased. At night sea sound which would have gone over your head in the day is now reaching you ear, directed there by the increased refractive index of the cooler air.


Here is similar case: sounds from the shore being louder to a person at sea than a person on the shore ...
http://www.school-for-champions.com/science/sound_over_water.htm

[LeeE]

I'm pretty sure that our hearing becomes more sensitive at night time.  This characteristic is believed to have evolved to help warn us about predators once the sun had gone down and when our vision was pretty useless, due to the lack of street lights at the time, or while asleep.

[lyner]

I think the 'refraction' arguments takes you the wrong way, in fact.
The speed of sound is higher in warmer air. When there is a temperature inversion (warm over cold air), sounds will be 'bent' towards the Earth.
It's the other way round where the sea, at night, is concerned. I'd expect the air just above the sea to be warmer than the air at greater height. This would mean that sounds would be deflected upwards, rather than downwards.
Also, there is a predominantly offshore wind at night, because the ground cools quicker than the sea; that, again, should 'bend the sounds' upwards, because of the velocity gradient. (Same reason as why sounds seem louder when 'blown towards you')

The wind nearly always drops at night, so the wind noise would drop - possibly making the waves sound louder.
 

[Don_1]

I think you will find that the sounds of the sea are no louder at night than during daylight. what makes it seem that way is the lack of other sounds when man and his noisy world go to bed, as do the birds and bees. You will find a similar effect in woodland. Man creates a great deal of noise which can travel over a considerable distance.

[paul.fr]

...Also, there is a predominantly offshore wind at night, because the ground cools quicker than the sea; that, again, should 'bend the sounds' upwards, because of the velocity gradient. (Same reason as why sounds seem louder when 'blown towards you')

The wind nearly always drops at night, so the wind noise would drop - possibly making the waves sound louder.
 

just to add to that:
The wind can blow stronger (on the coast) at night, especially if the land is hilly. Unless there is a storm in the offing then the sea is a relatively smooth surface, this allows the wind to blow stronger due to lack of friction. The windspeed for the coastal water can get as high as double that of coastal land.