when is the ocean surfaced heated or cooled from above?

Answer 1

There is no general answer to this question except to understand the processes involved. There are three ways the ocean surface heats and cools. They are:

1. Latent heat flux
2. Sensible heat flux
3. Radiative heat flux

The third can be subdivided into a longwave heat flux and a shortwave heat flux. The shortwave flux is always positive, because it is the radiation from the sun, meaning it heats the ocean. The longwave flux is the blackbody infrared radiation to/from the ocean surface and can be positive or negative, depending on the cloud cover.

The latent heat flux is nearly always negative and when it isn't negative it is essentially zero, meaning evaporation is always cooling the ocean.

The sensible heat flux can be positive or negative, depending on the air-water temperature difference.

It is simply incorrect to say that the ocean always heats during the day and cools at night. Depending on the local meteorology and sea surface temperature, you can have the ocean surface heating or cooling at any time of the day. For example, under cold, dry, cloud-free conditions the ocean surface can be cooling even at mid-day since the sum of the upward longwave radiative heat flux, the upward sensible heat flux, and the upward latent heat flux can be much larger than the downward shortwave radiative flux from solar insolation. Similarly, you can have a net downward transfer of heat (i.e., ocean warming) at night if the air temperature is warmer than the water, the skies are cloudy, and the relative humidity is high.

Answer 2

The ocean surface is heated by the sun.
It is cooled by the evaporation of the surface layers of water. It may also be cooled by floating ice or by cool winds blowing over the surface.

Answer 3

Ocean surface is heated from above during daytime and it is cooled from above during night time.