I have a car with a thermometer for the outside temperature. Where would they put the pickup that it wouldn’t be affected by the engine heat or wind chill when I am moving.
I don’t think “wind chill” changes the reading on a thermometer
I don’t know the answer to your question, however.
Temperature sensors on cars are typically mounted forward of the air intake or inside the side mirror housing and are shrouded from wind so as to get the ambient temperature unaffected by convective cooling of moving air. In my experience, the temperature readings are only accurate to within +/- 3 °C under good conditions, so I wouldn’t place a lot of credence in the reading.
Stranger
“Wind chill” only is relevant for warm-blooded animals, and refers to the idea that one’s environment seems colder than the air temperature would indicate. It is a specific instance of convective heat transfer, which in turn refers to situations in which objects are cooled or heated by their surrounding fluid medium. If an object is warmer than its environment, then a breeze helps cool it down faster than still air; animals and people who endure winter in the great plains states know all about this. However, if an object is cooler than its environment, then a breeze helps increase its temperature. In both situations, the wind can only move the object’s temperature closer to the air temperature, i.e. a cold thermometer will never become hotter than the air that’s blowing past it, and a hot thermometer will never become colder than the air that’s blowing past it.
The good news is that since air blowing past the thermometer helps it to accurately measure the air temperature, we can put it somewhere in the car’s slipstream - ideally somewhere ahead of the engine and any other heat sources. I don’t know specifically where that would be on a car, but it’s likely to be somewhere near the front bumper or grille, ahead (or at least away from) the radiator. If you have the service manual for your car (not the owner’s manual), it might tell you where it is.
As others have said, wind chill is not a factor. I wouldn’t have thought anywhere low down, such as the bumper, would be a good place, as it would be overexposed to heat radiating off the road surface. I have wondered where the sensor is before, as it generally seems accurate to within a degree or two on my car - although it does often over-read when I first start up the car, if it’s been in the sunshine, as you would expect.
In my late 80’s era Cadillac the outside air temperature sensor is located in the air intake. It is one of the parameters measured by the engine computer to determine how to run the engine. They also make it available on a display inside the car.
ETA: If the car has been sitting in a hot parking lot it will read high until you start driving and the moving air cools it down to the actual air temperature.
WHAT THE ?
A wet thermometer will suffer wind child, and it doesn’t have ANY blood.
Wind child is the cooling effect of (not 100% relative humid) wind due to increased evaporation.
Wind blowing past a wet thermometer will have a temperature drop because the water on the thermometer will evaporate. The evaporation absorbs heat cooling down the thermometer. Once all the water on the thermomoter has evaporated the reading will aprocach air temperature.
Some wind chill models incorporate evaporative cooling effects, but this is not universal, and it’s regarded as a secondary effect. The primary factors for calculating wind chill effect are wind speed and ambient temperature.
A wet thermometer may experience evaporative cooling, provided the ambient relative humidity isn’t very high. If it’s wet because it’s raining, there’s a good chance that ambient relative humidity is very high, and so the evaporative cooling effect will be minimal.
For some time I’ve wondered why folk put so much credence on specific temperature readings - in forecasts and such. Or when reading a thermometer before deciding whether to don a jacket.
I used to run over my lunch hour, but gave up on getting anything other than a very rough estimate of the temperature. Different websites would differ by several degrees (I imagine reflecting where the sensors were). I’d pass bank signs that varied by 10 degrees of more (Maybe the sun was hitting one, or maybe the other was just out of calibration.) Then as I ran to the lake and north or south, as the sun went behind a cloud, the temperature would vary 10 degrees or more.
Yet every night on the news they go on an on with such apparent precision, as tho than means anything to a person who is anywhere other than at the official recording site.
Personally, when I look at an outside thermometer, I pretty much view it in 5 degree increments. Doesn’t make a difference to me if it is 72 or 73 - I just consider it to be between 70-75. (Yeah, I know - that is a 6 degree increment!)
Although one common complaint about using the Celsius scale for temperature measurement is that it hax approximately half of the whole number increments as the Fahrenheit scale, the truth is that it is almost impossible for someone to accurately distinguish to less than +/-1 °C or +/-2 °F even under optimum conditions. Of course, what we really care about is the heating (or cooling) rate, which is dependant not only on the temperature of the ambient air (which primarily controls radiative heat transfer) but on the flow rate, density, and vapor content of the air (which controls convective heat transfer). This is why the same temperature at high altitudes is less effecting (the air can carry away less heat) and why San Francisco and Seattle feel much colder than inland cities at the same temperature (the water vapor content in the air is at or near sturation continuously). But stating radiative and convective heat flux is much less intuitive than ambient temperature.
Machine Elf is correct about wind chill factor; it is not a direct measurement of convective or evaporative cooling, but rather an attempt at quanifying the perceived equivalent ambient temperature for a given wind speed (and assumed density and vapor content, although these are not explicit factors in the analysis). It is calculated different ways by different meteorological bodies, and does not provide a one-to-one correspondence with actual temperature measurements.
Stranger
My educated guess is that the thermometer readout just uses a temperature signal supplied by engine control computer, which uses it to calculate air density.
No, it is a separate sensor that is usually somewhere behind the front bumper/fascia forward of the radiator. The location varies by model.
It looks like a little cone shaped plug. In the images in the following Google Image page you can see several and some of the locations on the vehicles.
Low down near the front bumper is actually a very good place. Its most important function is to warn you when the road surface is getting cold enough for ice to form. On my much prized Skoda Octavia VRS, a warning ping occurs when the sensed temperature drops below 4 deg C.
I don’t think so. If that were true, you would get a near instantaneous reading. In my truck, it takes a couple of miles for the temperature to register the difference between my (relatively) warm garage, and the cold outside air.
Most people don’t realize it, but temperature is a very hard thing to measure over a large area. As you’ve realized, it can vary wildly by location. You’ll almost always have a higher temperature in the city or airport than in the country or near a lake. There is a section of my town that feels good to drive by during the summer because on both sides of the road is a swampy area that always feels 10 degrees cooler.
My local media usually gives several temperatures from around the area in the weather roundup, or they will say “it’s X degrees here at the studio” or they will identify the location for the day’s highest temperature. But even then, it’s hard to say that’s 100% accurate.
The National Weather Service doesn’t certify their official temperatures until a few months later after they’ve been checked and adjusted for any local conditions that may have affected things. For example, a sensor at the airport may show several degrees higher than the other 10 thermometers in the area due to it’s location near a bunch of asphalt, so it may need to be adjusted down to give an idea of the actual air temperature. It’s more complicated than that, but that’s the idea. Only after the certification process can temperature be used in climate science or in court or wherever the true official temperature is important.