Why do temperature difference get bigger during clear nights in close distances?

[Vivaldi]

Why do temperature difference get bigger during clear nights in close distances?

[laly520]

during clear nights in close distances, temperature differences can get bigger due to a phenomenon called radiational cooling

[Vivaldi]

Very interesting.

[RavVid]

Clear skies allow infra red radiation to go to outer space whilst clouds reflect it back to earth. Clear skies mean lower night time temps and allow in max solar radiation during the day and therefore warmer.

[Vivaldi]

Also big difference in close distance

[handsomelad70]

The lack of cloud cover allows heat to escape into the atmosphere, causing minima (low temperatures) to be VASTLY chillier than maxima (high temperatures.)

[Vivaldi]

@handsomelad70

But why big difference in close distance?

[RavVid]

What do you mean in close distance? Are you saying there a large temperature differences 1 Km away or 500 m or 10 m in distance?

Black body radiation is going to cool during the night. But everything is about the same temperature , so will radiated (and cool the same).

If the pavement got hotter during the day than surroundings the the pavement would cool faster than the surroundings. The pavement and surroundings would become more equal and not more different.

That would be by radiation, by convection with the pavement heating air, and by conduction with the pavement heating the subsoil.

Just before dawn the pavement and surroundings will be the same temperature or very closely.

[Vivaldi]

2°C in 4 km for instance at the same elevation.

I measured with 2 thermometers together.

Going 2°C warmer. Returning 2°C colder.

[Vivaldi]

Also many times I did that.

2°C difference in 4 km.

[Vivaldi]

It is an open road.

There is no hill or anything in between. Flat.

[Vivaldi]

Sea elevation

[Vivaldi]

By open road, I meant no unevenness in between.

[RavVid]

OK 2 celsius difference at two points 4 K apart along a flat road. I presume you are measuring while driving a car. Clear nights are usually still nights with no wind and assuming still nights. For the air to be colder at a spot than it means the air has lost energy through radiation, convection or conduction or colder air has flowed to that point (really convection).

It is possible that chilled air collects at this point, there could be a land gradient that is not that apparent. The earth is not a black body; it is more of a gray body. It is plausible the amount of energy radiated varies over a 4 K distance due to buildings, trees grass etc. Water vapor in the air could be a factor as water vapor holds energy quite well (hence steam engines).

I don't think it is plausible to say why at this level of granularity

[Vivaldi]

Going and returning by bicycle

[Vivaldi]

I used 2 thermometers. Both chance by 2°C.

Going 2°C warmer. Returning 2°C colder.

Always like this at clear nights or little cloud.

[Vivaldi]

I had already mentioned about the 2 thermometer part. I forgot I mentioned it.

Since going is 2°C warmer and returning is 2°C colder. There is no time issue here.