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Apparent temperature is the temperature equivalent perceived by humans, caused by the combined effects of air temperature, relative humidity and wind speed. There are several ways of measuring it, personally I like the wet-bulb globe temperature as it combines the effects of radiation, humidity, temperature and wind speed on the perception of temperature. But there are other ways, such as heat index and wind chill factor.

Mars is very cold, with a mean temperature of −63 °C. But it's atmosphere is also very thin, at 0.00628 atm. This would strongly reduce the effects of wind chill but increase evaporation. But evaporation is easily countered with a suit.

So what would be the apparent temperature on Mars?

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    $\begingroup$ I don't think any measurement methods applicable on Earth are really applicable in pressures like on Mars. $\endgroup$ – SF. Sep 6 '17 at 9:55
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    $\begingroup$ Apparent temperature on Mars is probably a moot point. Another term for apparent temperature is "the temperature that it feels like". The temperature that we humans feel is based on the pocket of air around us. Wind, etc, disrupts said pocket of air to change the temperature we feel. Given that anyone who spends time on Mars will require a space suit, the temperature they feel will be that of the environment within the space suit. They will not be directly exposed to the Martian atmosphere. $\endgroup$ – Fred Sep 6 '17 at 12:18
  • $\begingroup$ Apparent temperature is not applicable to an astronaut wearing a space suit with active temperature control. No part of his skin is directly exposed to the atmosphere. $\endgroup$ – Uwe Sep 6 '17 at 14:58
  • $\begingroup$ A suit doesn't necessarily have temperature control. This is one of the suits that is proposed, and its more of a skintight onesie to compensate for the low pressure. But how quickly would you get cold? $\endgroup$ – Herman Sep 6 '17 at 15:10
  • $\begingroup$ A human at rest generates 70 to 100 W of heat. But under heavy work load, the heat may be 500 to 700 W. If the suit is not able to radiate this heat, the astronaut will overheat and could not do his work. On earth we may open, remove or close some parts of the clothes to adapt, but in a very thin atmosphere, the space suit should keep the astronaut at a temperature suitable to do his work. $\endgroup$ – Uwe Sep 6 '17 at 15:46
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A Google search for "mars thermal losses" brought me to a Science article introducing an American Meteorological Society paper: "Martian Windchill in Terrestrial Terms" by R. Osczevski. The idea appears to be the same one that Uwe's comment hints at: "wind chill" temperatures are reference temperatures that would cause the same heat loss, without winds, as the conditions you want to understand.

Table 2 in the article is a table of Earth Equivalent Temperatures. Based on a quick skim, the paper also discusses a couple of the model assumptions (which I believe to be made intentionally the same as Earthly windchill model assumptions): emissivity and internal thermal resistance, and how varying those parameters effects the Earth Equivalent Temperature.

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  • $\begingroup$ A this is exactly what I was looking for. So the tropics are like England and the planet average like a Minnesota winter. Those are pretty gentle and livable temperatures. $\endgroup$ – Herman Sep 12 '17 at 6:51
  • $\begingroup$ There is still a very cold ball of rock that's way more thermally conductive than its atmosphere, so you can't completely forget the actual temperature, but the air does seem alright. $\endgroup$ – Erin Anne Sep 12 '17 at 13:25
  • $\begingroup$ No going outside without mah boots then. $\endgroup$ – Herman Sep 13 '17 at 14:31

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