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https://www.weather.gov/ama/heatindex

What is the heat index?

"온도가 높은 것이 아니라, 습도가 높은 것입니다." 
여름에 들어보아보았을 문구지만, 실제로는 둘 다입니다. 
실질적 온도라고도하는 열 지수는 상대 습도가 대기 온도와 결합 될 때 온도가 인체에 미치는 느낌입니다. 
이것은 인체의 편안함을 고려한 것입니다. 몸이 너무 뜨거워지면 땀을 흘리거나 땀이 나기 시작합니다. 
땀이 증발 할 수 없으면 신체 온도를 조절할 수 없습니다. 증발은 냉각 과정입니다. 
땀이 몸에서 증발하면 효과적으로 체온을 줄입니다. 
대기 수분 함량 (즉, 상대 습도)이 높을 때 신체의 증발 속도가 감소합니다. 
다시 말해, 인체는 습한 환경에서 더 따뜻하게 느껴집니다. 
땀 속도가 증가하여 상대 습도가 감소하면 반대의 경우도 마찬가지입니다. 
건조한 환경에서는 실제로 몸이 시원해집니다. 
대기 온도와 상대 습도와 열 지수 사이에는 직접적인 관계가 있습니다. 
이는 대기 온도와 상대 습도가 증가 (감소)하고 열 지수가 증가 (감소)한다는 의미입니다.

https://www.wpc.ncep.noaa.gov/html/heatindex_equation.shtml

The Heat Index Equation

The computation of the heat index is a refinement of a result obtained by multiple regression analysis carried out by Lans P. Rothfusz and described in a 1990 National Weather Service (NWS) Technical Attachment (SR 90-23).  The regression equation of Rothfusz is

HI = -42.379 + 2.04901523*T + 10.14333127*RH - .22475541*T*RH - .00683783*T*T - .05481717*RH*RH + .00122874*T*T*RH + .00085282*T*RH*RH - .00000199*T*T*RH*RH

where T is temperature in degrees F and RH is relative humidity in percent.  HI is the heat index expressed as an apparent temperature in degrees F.  If the RH is less than 13% and the temperature is between 80 and 112 degrees F, then the following adjustment is subtracted from HI:

ADJUSTMENT = [(13-RH)/4]*SQRT{[17-ABS(T-95.)]/17}

where ABS and SQRT are the absolute value and square root functions, respectively.  On the other hand, if the RH is greater than 85% and the temperature is between 80 and 87 degrees F, then the following adjustment is added to HI:

ADJUSTMENT = [(RH-85)/10] * [(87-T)/5]

The Rothfusz regression is not appropriate when conditions of temperature and humidity warrant a heat index value below about 80 degrees F. In those cases, a simpler formula is applied to calculate values consistent with Steadman's results:

HI = 0.5 * {T + 61.0 + [(T-68.0)*1.2] + (RH*0.094)}

In practice, the simple formula is computed first and the result averaged with the temperature. If this heat index value is 80 degrees F or higher, the full regression equation along with any adjustment as described above is applied.

The Rothfusz regression is not valid for extreme temperature and relative humidity conditions beyond the range of data considered by Steadman.

계산기

https://www.wpc.ncep.noaa.gov/html/heatindex.shtml