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So I was in this place called Chamundi hills, Mysore.
I was riding back at around 7pm down hill and noticed this strange behavior. About every 50-100 meters the temperature fluctuated.
It was extremely cold in some areas and in the next 100 meters I could feel the warmth. The whole cycle repeated all the way (about 8-10 kilometers).
Is there any scientific explanation about this?
To extend @Poutnik's invisible river analogy, the cold air can also 'pool' in small dips.
On clear nights, temperature fluctuations are quite a frequent occurrence due to radiative cooling. If the air cools sufficiently to reach the dew point, then cloud can act as a 'tracer' for the air pockets.
An example of this are fog patches that you potentially pass through in certain conditions. The air in the fog patches is a little colder (or higher absolute humidity, for example over a lake) than the surrounding fog-free areas. Even if the air wasn't cold enough to form cloud, the same temperature variation can occur invisibly.
Here's an example from Wikimedia user Simo Räsänen:
In the mountains, the invisible rivers of cold, descending air that @Poutnik mentions can sometimes be seen by tracer clouds flowing down hillsides. Colder air is denser than the surrounding air and has less friction so gravity pulls it down. The areas with cloud will be colder than the adjacent cloud-free zones. This effect can lead to strong down-slope katabatic winds. In Antarctica this effect is responsible for some of the strongest winds in the world.
Here's a good example from Wikimedia user Andrew J. Kurbiko:
To summarise, the key to the effect you noticed is almost certainly radiative cooling and the movement of colder denser air. Radiative cooling occurs due to any object above absolute zero giving off radiation. On a clear night this radiation passes through the Earth's atmosphere and is lost into space. This cools down the object (land) that the radiation came from. The land, in turn, cools down the air above it. On a cloudy night, the radiation is reflected by the clouds and reabsorbed by the land keeping the temperature constant.
I assume local downstream flows of cold air near surface, that got cool down by surface radiation on the hill slopes. You can imagine it as invisible rivers of cold, descending air.
Yes, there could be several reasons for the temperature fluctuation you experienced. Some possible explanations are:
Altitude change: As you were riding downhill, you may have experienced changes in altitude, which can affect temperature.
Microclimates: Different areas of the hill may have their own microclimates, with different temperatures and humidity levels, which could explain the fluctuations you experienced.
Air currents: The movement of air currents can also cause temperature fluctuations, as warm air rises and cold air sinks.
Shadows: Shadows cast by buildings, trees, or other obstacles can also affect temperature, as they can block the sun's warmth.
Localized heating: Localized heating sources, such as factories or power plants, can also affect temperature in a specific area.
It's possible that a combination of these factors contributed to the temperature fluctuations you experienced.
Something I have observed more than once: Katabatic and anabatic winds tend to follow drainage patterns--there's more air flow when you're lined up with the terrain. Even when you don't feel the wind it can change the air temperature.
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