So, I made a less-than-earth shattering observation after running around outside yesterday and last night–even though the actual temperature hadn’t changed that much, it felt a lot colder at night (probably has something to do with that large nurning orb not throwing heat rays on my ass).
Is there a way to express the difference in a “feels like” term, like the wind chill factor for windy days? I.e., can you say that 45 degrees at night feels like 30 during the day? Or I suppose it could just all be in my head and the actual perceived temperature doesn’t really change. What say you, dope?
That seems backwards to me. My understanding was that temperatures are generally measured “in the shade”, so you would have to add a “sunshine warming factor” to get the temperature in full sunlight (rather than subtracting a “no-sun chill factor” to get the temperature in no sunlight, as you suggest).
Seconding hogarth, and adding that it would also need to account for the color and type of clothing you are wearing. Stark naked, standing in the sun will warm you less than wearing a nice dark suit, standing in the sun. Then there’s the “cloudy day” correction factor, with a correction of its own for just how heavy the clouds are… etc. etc. This could get to be a ridiculously complicated “warming factor”.
I’d expect the night-time chill factor would depend on whether it’s a clear night sky versus an overcast one. The overcast sky acts as a blanket, keeping the Earth’s heat in, while the clear sky lets it radiate away. Something covered, like in a car port, wouldn’t see the cold sky, and would be less affected, similar to the way something in the shade (say, under a car port) is less affected by the Sun.
I’d think your night time chill factor would be related to how fast the temperature is dropping overnight. If the sky wasn’t changing overnight (i.e. clear all night, or overcast all night), you could probably relate that to the expected overnight low.
Here is a weather station. It’s the white box in the foreground, which as you can see, is indeed well-ventilated (and provides shade for the instruments within).
It is not just the sun warming you during the day. On a clear night, you are warming space, and losing heat to do so. If you were not able to convert food calories to heat, you could actually become cooler than the air. This is what causes frost and dew to form on plants and other objects: They radiate their heat to space and become cooler than the air. This cools the air near them and the moisture in the air condenses and/or freezes on the surface.
There are several ways to slow the heat loss due to radiation:
1)Place an optical barrier between yourself and space. Clouds work well for this even just a light haze helps, as it blocks IR more than visible light. A tarp will work, which is why gardeners cover their tomato plants at night in the fall. Most window glass is pretty opaque at IR as well, which is why greenhouses work. Smoke works well, and smudge pots in vineyards generate smoke as well as heat. A roof works well. Carports will stop most frost from forming on your car. Lack of clouds and moisture to form haze is why it gets so freakishly cold in the desert at night. From Albuquerque, I can normally see Mt.Taylor 70 miles away. In the midwest, it is common that haze limits visibility to 5 or 10 miles.
2)If you blow the air past the objects, they won’t be able to cool much below the air temperature. This works well for preventing plants from frosting. Orchards are frequently sited at the mouth of canyons to take advantage of nocturnal winds. Failing that, large electric motor or engine driven fans (wind machines) can be used to prevent frosting. Warming things with wind seems counterintuitive, but that is only because humans mostly have a body temperature greater than common air temperatures, and we are equipped for evaporative cooling (sweat) Blowing 40F air on you tomatos really will keep them from frosting, even if it makes you shiver.
3)A heat source nearby. Campfires and electric or gas IR heaters are obvious, but this doesn’t have to be an active source. Large rocks will hold the heat of the day, and release it over time. Bodies of water will do even better. Putting old tires around your tomato plants is an old gardeners trick. Brick or adobe walls will serve. Smudge pots in vineyards put out heat and smoke, and the smoke helps block radiation.
