From bf844972aad8839d430be88b14097fd4cdaec059 Mon Sep 17 00:00:00 2001 From: Igor Pashev Date: Wed, 12 May 2021 16:34:03 +0200 Subject: Show absolute humidity --- lib/Web/OpenWeatherMap/Formulas.hs | 37 +++++++++++++++++++++++++++++++++++++ 1 file changed, 37 insertions(+) create mode 100644 lib/Web/OpenWeatherMap/Formulas.hs (limited to 'lib/Web/OpenWeatherMap') diff --git a/lib/Web/OpenWeatherMap/Formulas.hs b/lib/Web/OpenWeatherMap/Formulas.hs new file mode 100644 index 0000000..f63bc9f --- /dev/null +++ b/lib/Web/OpenWeatherMap/Formulas.hs @@ -0,0 +1,37 @@ +{-# LANGUAGE NamedFieldPuns #-} + +module Web.OpenWeatherMap.Formulas + ( absoluteHumidity + ) where + +import Web.OpenWeatherMap.Types.Main + +{-- | Calculate absolute humidity (g/m³) + +Returns 'Nothing' if the temperature is out of range (−30°C, +35°C). + +-} +absoluteHumidity :: Main -> Maybe Double +absoluteHumidity Main {temp, humidity} + | tC > -30 && tC < 35 = Just $ ahBolton1980 temp humidity + | otherwise = Nothing + where + tC = k2c temp + +{-- | Calculate absolute humidity (g/m³) + +Ref.: Bolton D. "The Computation of Equivalent Potential Temperature", +Monthly Weather Review, 1980, 108(7):1046–1053. + +-} +ahBolton1980 :: + Double -- ^ Temperature in Kelvins + -> Double -- ^ Relative humidity in % + -> Double +ahBolton1980 temp humidity = + 13.25 * humidity * exp (17.67 * tC / (tC + 243.5)) / temp + where + tC = k2c temp + +k2c :: Double -> Double +k2c t = t - 273.15 -- cgit v1.2.3