Merge branch '15-humidity-conversions' into 'master'

Resolve "humidity conversions"

Closes #15

See merge request !25

radixio/gfsfile.cc

@@ -843,6 +843,18 @@ std::vector<std::vector<float>> GFSFile::query(float lat, float lon, int month,
       {
         surfaceAltitude = hpaToAltitude(vdata[kk][ll], temp, msle) - 2.f;
       }
+      // check whether relative humidity has been requested, and convert
+      // specific humidity if this is present instead
+      auto relHumIt = std::find(columns.begin(), columns.end(), "RELH");
+      if (relHumIt != columns.end() && varb.compare("SPHU") == 0)
+      {
+        varb                    = "RELH";
+        double specificHumidity = vdata[kk][ll];
+        // Convert specific humidity to relative humidity
+        vdata[kk][ll] =
+            specificHumidityToRelativeHumidity(specificHumidity, temp, plevel);
+      }
+
       auto it = std::find(columns.begin(), columns.end(), varb);
       if (it != columns.end())
       {

radixmath/constants.hh

@@ -39,6 +39,8 @@ const Real sqrtTHREE        = std::sqrt(Real(3.0));
 const Real DAYS_PER_YEAR    = 365.25;
 const Real SECONDS_PER_HOUR = 3600.0;
 const Real METERS_PER_MILE  = 1609.344;
+const Real ABS_ZERO_CELSIUS = -273.15;
+const Real MASS_RATIO_WATER_VAPOR_DRY_AIR = 0.62198;
 /**
  * Type def unsigned long to Identifier
  */

radixmath/tests/tstUtil.cc

@@ -198,3 +198,404 @@ TEST(radix, greatCircleVolume)
                                     EARTH_RADIUS_MEAN + 1);
   EXPECT_NEAR(24625680, volume, 1e-1);
 }
+
+TEST(radix, Pressure1000)
+{
+  double tolerance = 0.001;
+
+  double potentialTemp1 = 273.15, potentialTemp2 = 293.0,
+         potentialTemp3 = 240.654, pressure = 1000;
+
+  double temp = absoluteTemperature(potentialTemp1, pressure);
+  ASSERT_NEAR(potentialTemp1, temp, potentialTemp1 * tolerance);
+
+  temp = absoluteTemperature(potentialTemp2, pressure);
+  ASSERT_NEAR(potentialTemp2, temp, potentialTemp2 * tolerance);
+
+  temp = absoluteTemperature(potentialTemp3, pressure);
+  ASSERT_NEAR(potentialTemp3, temp, potentialTemp3 * tolerance);
+}
+
+TEST(radix, Pressure900)
+{
+  double tolerance = 0.001;
+
+  double potentialTemp1 = 273.15, potentialTemp2 = 293.0,
+         potentialTemp3 = 240.654, pressure = 900;
+
+  double expectTemp1 = 265.042, expectTemp2 = 284.303, expectTemp3 = 233.511;
+
+  double temp = absoluteTemperature(potentialTemp1, pressure);
+  ASSERT_NEAR(expectTemp1, temp, expectTemp1 * tolerance);
+
+  temp = absoluteTemperature(potentialTemp2, pressure);
+  ASSERT_NEAR(expectTemp2, temp, expectTemp2 * tolerance);
+
+  temp = absoluteTemperature(potentialTemp3, pressure);
+  ASSERT_NEAR(expectTemp3, temp, expectTemp3 * tolerance);
+}
+
+TEST(radix, Pressure800)
+{
+  double tolerance = 0.001;
+
+  double potentialTemp1 = 273.15, potentialTemp2 = 293.0,
+         potentialTemp3 = 240.654, pressure = 800;
+
+  double expectTemp1 = 256.2624306593, expectTemp2 = 274.8851992794,
+         expectTemp3 = 225.7755042573;
+
+  double temp = absoluteTemperature(potentialTemp1, pressure);
+  ASSERT_NEAR(expectTemp1, temp, expectTemp1 * tolerance);
+
+  temp = absoluteTemperature(potentialTemp2, pressure);
+  ASSERT_NEAR(expectTemp2, temp, expectTemp2 * tolerance);
+
+  temp = absoluteTemperature(potentialTemp3, pressure);
+  ASSERT_NEAR(expectTemp3, temp, expectTemp3 * tolerance);
+}
+
+TEST(radix, Pressure700)
+{
+  double tolerance = 0.001;
+
+  double potentialTemp1 = 273.15, potentialTemp2 = 293.0,
+         potentialTemp3 = 240.654, pressure = 700;
+
+  double expectTemp1 = 246.6602937075, expectTemp2 = 264.5852683737,
+         expectTemp3 = 217.3157104956;
+
+  double temp = absoluteTemperature(potentialTemp1, pressure);
+  ASSERT_NEAR(expectTemp1, temp, expectTemp1 * tolerance);
+
+  temp = absoluteTemperature(potentialTemp2, pressure);
+  ASSERT_NEAR(expectTemp2, temp, expectTemp2 * tolerance);
+
+  temp = absoluteTemperature(potentialTemp3, pressure);
+  ASSERT_NEAR(expectTemp3, temp, expectTemp3 * tolerance);
+}
+
+TEST(radix, Pressure600)
+{
+  double tolerance = 0.001;
+
+  double potentialTemp1 = 273.15, potentialTemp2 = 293.0,
+         potentialTemp3 = 240.654, pressure = 600;
+
+  double expectTemp1 = 236.0219871191, expectTemp2 = 253.1738686651,
+         expectTemp3 = 207.9430177124;
+
+  double temp = absoluteTemperature(potentialTemp1, pressure);
+  ASSERT_NEAR(expectTemp1, temp, expectTemp1 * tolerance);
+
+  temp = absoluteTemperature(potentialTemp2, pressure);
+  ASSERT_NEAR(expectTemp2, temp, expectTemp2 * tolerance);
+
+  temp = absoluteTemperature(potentialTemp3, pressure);
+  ASSERT_NEAR(expectTemp3, temp, expectTemp3 * tolerance);
+}
+
+TEST(radix, Pressure500)
+{
+  double tolerance = 0.001;
+
+  double potentialTemp1 = 273.15, potentialTemp2 = 293.0,
+         potentialTemp3 = 240.654, pressure = 500;
+
+  double expectTemp1 = 224.0302306934, expectTemp2 = 240.3106629806,
+         expectTemp3 = 197.3778917711;
+
+  double temp = absoluteTemperature(potentialTemp1, pressure);
+  ASSERT_NEAR(expectTemp1, temp, expectTemp1 * tolerance);
+
+  temp = absoluteTemperature(potentialTemp2, pressure);
+  ASSERT_NEAR(expectTemp2, temp, expectTemp2 * tolerance);
+
+  temp = absoluteTemperature(potentialTemp3, pressure);
+  ASSERT_NEAR(expectTemp3, temp, expectTemp3 * tolerance);
+}
+
+TEST(radix, Pressure400)
+{
+  double tolerance = 0.001;
+
+  double potentialTemp1 = 273.15, potentialTemp2 = 293.0,
+         potentialTemp3 = 240.654, pressure = 400;
+
+  double expectTemp1 = 210.1795037842, expectTemp2 = 225.4533941379,
+         expectTemp3 = 185.1749526036;
+
+  double temp = absoluteTemperature(potentialTemp1, pressure);
+  ASSERT_NEAR(expectTemp1, temp, expectTemp1 * tolerance);
+
+  temp = absoluteTemperature(potentialTemp2, pressure);
+  ASSERT_NEAR(expectTemp2, temp, expectTemp2 * tolerance);
+
+  temp = absoluteTemperature(potentialTemp3, pressure);
+  ASSERT_NEAR(expectTemp3, temp, expectTemp3 * tolerance);
+}
+
+TEST(radix, Pressure300)
+{
+  double tolerance = 0.001;
+
+  double potentialTemp1 = 273.15, potentialTemp2 = 293.0,
+         potentialTemp3 = 240.654, pressure = 300;
+
+  double expectTemp1 = 193.5788402819, expectTemp2 = 207.646348902,
+         expectTemp3 = 170.5492302002;
+
+  double temp = absoluteTemperature(potentialTemp1, pressure);
+  ASSERT_NEAR(expectTemp1, temp, expectTemp1 * tolerance);
+
+  temp = absoluteTemperature(potentialTemp2, pressure);
+  ASSERT_NEAR(expectTemp2, temp, expectTemp2 * tolerance);
+
+  temp = absoluteTemperature(potentialTemp3, pressure);
+  ASSERT_NEAR(expectTemp3, temp, expectTemp3 * tolerance);
+}
+
+TEST(radix, Pressure200)
+{
+  double tolerance = 0.001;
+
+  double potentialTemp1 = 273.15, potentialTemp2 = 293.0,
+         potentialTemp3 = 240.654, pressure = 200;
+
+  double expectTemp1 = 172.3835354925, expectTemp2 = 184.9107666092,
+         expectTemp3 = 151.8754799576;
+
+  double temp = absoluteTemperature(potentialTemp1, pressure);
+  ASSERT_NEAR(expectTemp1, temp, expectTemp1 * tolerance);
+
+  temp = absoluteTemperature(potentialTemp2, pressure);
+  ASSERT_NEAR(expectTemp2, temp, expectTemp2 * tolerance);
+
+  temp = absoluteTemperature(potentialTemp3, pressure);
+  ASSERT_NEAR(expectTemp3, temp, expectTemp3 * tolerance);
+}
+
+TEST(radix, MixingRatio10)
+{
+  double tolerance = 0.01;
+
+  double temp1 = 25 - ABS_ZERO_CELSIUS, pressure1 = 900.0,
+         temp2 = 10 - ABS_ZERO_CELSIUS, pressure2 = 650.0,
+         temp3 = 40 - ABS_ZERO_CELSIUS, pressure3 = 800.0,
+         mixingRatio = 10.0 * 1.0E-3;
+
+  double expectRelHum1 = 44.967, expectRelHum2 = 83.818, expectRelHum3 = 17.158;
+
+  double relHum = mixingRatioToRelativeHumidity(mixingRatio, temp1, pressure1);
+  ASSERT_NEAR(expectRelHum1, relHum, expectRelHum1 * tolerance);
+
+  relHum = mixingRatioToRelativeHumidity(mixingRatio, temp2, pressure2);
+  ASSERT_NEAR(expectRelHum2, relHum, expectRelHum2 * tolerance);
+
+  relHum = mixingRatioToRelativeHumidity(mixingRatio, temp3, pressure3);
+  ASSERT_NEAR(expectRelHum3, relHum, expectRelHum3 * tolerance);
+}
+
+TEST(radix, MixingRatio5)
+{
+  double tolerance = 0.01;
+
+  double temp1 = 5.3 - ABS_ZERO_CELSIUS, pressure1 = 1010.0,
+         temp2 = -3.2 - ABS_ZERO_CELSIUS, pressure2 = 740.0,
+         temp3 = 0.0 - ABS_ZERO_CELSIUS, pressure3 = 300.0,
+         mixingRatio = 5.0 * 1.0E-3;
+
+  double expectRelHum1 = 90.474, expectRelHum2 = 100.0, expectRelHum3 = 39.17;
+
+  double relHum = mixingRatioToRelativeHumidity(mixingRatio, temp1, pressure1);
+  ASSERT_NEAR(expectRelHum1, relHum, expectRelHum1 * tolerance);
+
+  relHum = mixingRatioToRelativeHumidity(mixingRatio, temp2, pressure2);
+  ASSERT_NEAR(expectRelHum2, relHum, expectRelHum2 * tolerance);
+
+  relHum = mixingRatioToRelativeHumidity(mixingRatio, temp3, pressure3);
+  ASSERT_NEAR(expectRelHum3, relHum, expectRelHum3 * tolerance);
+}
+
+TEST(radix, MixingRatio3)
+{
+  double tolerance = 0.01;
+
+  double temp1 = -2.0 - ABS_ZERO_CELSIUS, pressure1 = 890.0,
+         temp2 = -3.2 - ABS_ZERO_CELSIUS, pressure2 = 550.0,
+         temp3 = -15.0 - ABS_ZERO_CELSIUS, pressure3 = 300.0,
+         mixingRatio = 3.0 * 1.0E-3;
+
+  double expectRelHum1 = 81.01, expectRelHum2 = 54.73, expectRelHum3 = 75.34;
+
+  double relHum = mixingRatioToRelativeHumidity(mixingRatio, temp1, pressure1);
+  ASSERT_NEAR(expectRelHum1, relHum, expectRelHum1 * tolerance);
+
+  relHum = mixingRatioToRelativeHumidity(mixingRatio, temp2, pressure2);
+  ASSERT_NEAR(expectRelHum2, relHum, expectRelHum2 * tolerance);
+
+  relHum = mixingRatioToRelativeHumidity(mixingRatio, temp3, pressure3);
+  ASSERT_NEAR(expectRelHum3, relHum, expectRelHum3 * tolerance);
+}
+
+TEST(radix, MixingRatio1)
+{
+  double tolerance = 0.01;
+
+  double temp1 = 6.0 - ABS_ZERO_CELSIUS, pressure1 = 890.0,
+         temp2 = 1.5 - ABS_ZERO_CELSIUS, pressure2 = 550.0,
+         temp3 = -25.0 - ABS_ZERO_CELSIUS, pressure3 = 300.0,
+         mixingRatio = 1.0 * 1.0E-3;
+
+  double expectRelHum1 = 15.29, expectRelHum2 = 12.971, expectRelHum3 = 59.66;
+
+  double relHum = mixingRatioToRelativeHumidity(mixingRatio, temp1, pressure1);
+  ASSERT_NEAR(expectRelHum1, relHum, expectRelHum1 * tolerance);
+
+  relHum = mixingRatioToRelativeHumidity(mixingRatio, temp2, pressure2);
+  ASSERT_NEAR(expectRelHum2, relHum, expectRelHum2 * tolerance);
+
+  relHum = mixingRatioToRelativeHumidity(mixingRatio, temp3, pressure3);
+  ASSERT_NEAR(expectRelHum3, relHum, expectRelHum3 * tolerance);
+}
+
+TEST(radix, MixingRatioPoint25)
+{
+  double tolerance = 0.01;
+
+  double temp1 = 32.0 - ABS_ZERO_CELSIUS, pressure1 = 1050.0,
+         temp2 = 6.5 - ABS_ZERO_CELSIUS, pressure2 = 650.0,
+         temp3 = -25.0 - ABS_ZERO_CELSIUS, pressure3 = 250.0,
+         mixingRatio = 0.25 * 1.0E-3;
+
+  double expectRelHum1 = 0.88722, expectRelHum2 = 2.6997, expectRelHum3 = 12.44;
+
+  double relHum = mixingRatioToRelativeHumidity(mixingRatio, temp1, pressure1);
+  ASSERT_NEAR(expectRelHum1, relHum, expectRelHum1 * tolerance);
+
+  relHum = mixingRatioToRelativeHumidity(mixingRatio, temp2, pressure2);
+  ASSERT_NEAR(expectRelHum2, relHum, expectRelHum2 * tolerance);
+
+  relHum = mixingRatioToRelativeHumidity(mixingRatio, temp3, pressure3);
+  ASSERT_NEAR(expectRelHum3, relHum, expectRelHum3 * tolerance);
+}
+
+TEST(radix, SpecificHumidity10)
+{
+  double tolerance = 0.01;
+
+  double temp1 = 25 - ABS_ZERO_CELSIUS, pressure1 = 900.0,
+         temp2 = 10 - ABS_ZERO_CELSIUS, pressure2 = 650.0,
+         temp3 = 40 - ABS_ZERO_CELSIUS, pressure3 = 800.0,
+         specificHumidity = 10.0;
+
+  double expectRelHum1 = 44.967, expectRelHum2 = 83.818, expectRelHum3 = 17.158;
+
+  double relHum =
+      specificHumidityToRelativeHumidity(specificHumidity, temp1, pressure1);
+  ASSERT_NEAR(expectRelHum1, relHum, expectRelHum1 * tolerance);
+
+  relHum =
+      specificHumidityToRelativeHumidity(specificHumidity, temp2, pressure2);
+  ASSERT_NEAR(expectRelHum2, relHum, expectRelHum2 * tolerance);
+
+  relHum =
+      specificHumidityToRelativeHumidity(specificHumidity, temp3, pressure3);
+  ASSERT_NEAR(expectRelHum3, relHum, expectRelHum3 * tolerance);
+}
+
+TEST(radix, SpecificHumidity5)
+{
+  double tolerance = 0.01;
+
+  double temp1 = 5.3 - ABS_ZERO_CELSIUS, pressure1 = 1010.0,
+         temp2 = -3.2 - ABS_ZERO_CELSIUS, pressure2 = 740.0,
+         temp3 = 0.0 - ABS_ZERO_CELSIUS, pressure3 = 300.0,
+         specificHumidity = 5.0;
+
+  double expectRelHum1 = 90.474, expectRelHum2 = 100.0, expectRelHum3 = 39.17;
+
+  double relHum =
+      specificHumidityToRelativeHumidity(specificHumidity, temp1, pressure1);
+  ASSERT_NEAR(expectRelHum1, relHum, expectRelHum1 * tolerance);
+
+  relHum =
+      specificHumidityToRelativeHumidity(specificHumidity, temp2, pressure2);
+  ASSERT_NEAR(expectRelHum2, relHum, expectRelHum2 * tolerance);
+
+  relHum =
+      specificHumidityToRelativeHumidity(specificHumidity, temp3, pressure3);
+  ASSERT_NEAR(expectRelHum3, relHum, expectRelHum3 * tolerance);
+}
+
+TEST(radix, SpecificHumidity3)
+{
+  double tolerance = 0.01;
+
+  double temp1 = -2.0 - ABS_ZERO_CELSIUS, pressure1 = 890.0,
+         temp2 = -3.2 - ABS_ZERO_CELSIUS, pressure2 = 550.0,
+         temp3 = -15.0 - ABS_ZERO_CELSIUS, pressure3 = 300.0,
+         specificHumidity = 3.0;
+
+  double expectRelHum1 = 81.01, expectRelHum2 = 54.73, expectRelHum3 = 75.34;
+
+  double relHum =
+      specificHumidityToRelativeHumidity(specificHumidity, temp1, pressure1);
+  ASSERT_NEAR(expectRelHum1, relHum, expectRelHum1 * tolerance);
+
+  relHum =
+      specificHumidityToRelativeHumidity(specificHumidity, temp2, pressure2);
+  ASSERT_NEAR(expectRelHum2, relHum, expectRelHum2 * tolerance);
+
+  relHum =
+      specificHumidityToRelativeHumidity(specificHumidity, temp3, pressure3);
+  ASSERT_NEAR(expectRelHum3, relHum, expectRelHum3 * tolerance);
+}
+
+TEST(radix, SpecificHumidity1)
+{
+  double tolerance = 0.01;
+
+  double temp1 = 6.0 - ABS_ZERO_CELSIUS, pressure1 = 890.0,
+         temp2 = 1.5 - ABS_ZERO_CELSIUS, pressure2 = 550.0,
+         temp3 = -25.0 - ABS_ZERO_CELSIUS, pressure3 = 300.0,
+         specificHumidity = 1.0;
+
+  double expectRelHum1 = 15.29, expectRelHum2 = 12.971, expectRelHum3 = 59.66;
+
+  double relHum =
+      specificHumidityToRelativeHumidity(specificHumidity, temp1, pressure1);
+  ASSERT_NEAR(expectRelHum1, relHum, expectRelHum1 * tolerance);
+
+  relHum =
+      specificHumidityToRelativeHumidity(specificHumidity, temp2, pressure2);
+  ASSERT_NEAR(expectRelHum2, relHum, expectRelHum2 * tolerance);
+
+  relHum =
+      specificHumidityToRelativeHumidity(specificHumidity, temp3, pressure3);
+  ASSERT_NEAR(expectRelHum3, relHum, expectRelHum3 * tolerance);
+}
+
+TEST(radix, SpecificHumidityPoint25)
+{
+  double tolerance = 0.01;
+
+  double temp1 = 32.0 - ABS_ZERO_CELSIUS, pressure1 = 1050.0,
+         temp2 = 6.5 - ABS_ZERO_CELSIUS, pressure2 = 650.0,
+         temp3 = -25.0 - ABS_ZERO_CELSIUS, pressure3 = 250.0,
+         specificHumidity = 0.25;
+
+  double expectRelHum1 = 0.88722, expectRelHum2 = 2.6997, expectRelHum3 = 12.44;
+
+  double relHum =
+      specificHumidityToRelativeHumidity(specificHumidity, temp1, pressure1);
+  ASSERT_NEAR(expectRelHum1, relHum, expectRelHum1 * tolerance);
+
+  relHum =
+      specificHumidityToRelativeHumidity(specificHumidity, temp2, pressure2);
+  ASSERT_NEAR(expectRelHum2, relHum, expectRelHum2 * tolerance);
+
+  relHum =
+      specificHumidityToRelativeHumidity(specificHumidity, temp3, pressure3);
+  ASSERT_NEAR(expectRelHum3, relHum, expectRelHum3 * tolerance);
+}

radixmath/util.cc

@@ -228,4 +228,75 @@ double exponentialIntegral(double d)
   return numer / denom / (d * std::exp(d));
 }
 
+Real absoluteTemperature(Real potentialTemp, Real pressure)
+{
+  // Gas constant / specific heat capacity at constant pressure for air
+  double rDivCp = 0.286;
+
+  // Reference pressure (mb)
+  double refPressure = 1000.0;
+
+  double expComponent = pow((refPressure / pressure), rDivCp);
+
+  double temp = potentialTemp / expComponent;
+
+  return temp;
+}
+
+Real saturationVaporPressure(Real absTemp, Real pressure)
+{
+  // Convert temperature to C and limit range to -45 < temp < +60
+  double tempC = absTemp + ABS_ZERO_CELSIUS;
+  tempC        = std::max(-45.0, std::min(60.0, tempC));
+
+  // Calculate saturation vapour pressure
+  double satVapPress = 6.112 * exp(17.62 * tempC / (243.12 + tempC));
+
+  // Apply correction for moist air
+  double moistCorrection =
+      1.0 + (4.5 + 0.0006 * pow(tempC, 2)) * pressure * 1.0E-6;
+  satVapPress = satVapPress * moistCorrection;
+
+  return satVapPress;
+}
+
+Real mixingRatioToRelativeHumidity(Real mixingRatio, Real absTemp,
+                                   Real pressure)
+{
+  // Calculate the saturation vapour pressure
+  double satVapPress = saturationVaporPressure(absTemp, pressure);
+
+  // Calculate the vapour pressure
+  double vapPress =
+      mixingRatio / (MASS_RATIO_WATER_VAPOR_DRY_AIR + mixingRatio) * pressure;
+
+  // Calculate the relative humidity - ensure it is 0 < humidity < 100
+  double relHum = 100.0 * vapPress / satVapPress;
+  relHum        = std::max(0.0, std::min(100.0, relHum));
+
+  return relHum;
+}
+
+Real specificHumidityToRelativeHumidity(Real specificHumidity, Real absTemp,
+                                        Real pressure)
+{
+  // Convert input specific humidity from g/kg to kg/kg
+  specificHumidity = specificHumidity / 1000.0;
+
+  // Calculate the saturation vapour pressure
+  double satVapPress = saturationVaporPressure(absTemp, pressure);
+
+  // Calculate the vapour pressure
+  double vapPress = specificHumidity /
+                    (MASS_RATIO_WATER_VAPOR_DRY_AIR +
+                     (1 - MASS_RATIO_WATER_VAPOR_DRY_AIR) * specificHumidity) *
+                    pressure;
+
+  // Calculate the relative humidity - ensure it is 0 < humidity < 100
+  double relHum = 100.0 * vapPress / satVapPress;
+  relHum        = std::max(0.0, std::min(100.0, relHum));
+
+  return relHum;
+}
+
 }  // namespace radix

radixmath/util.hh

@@ -18,7 +18,7 @@
 namespace radix
 {
 /**
- * @brief hpaToAltitude converts hectorpascals or millibars to altitude (meters)
+ * @brief hpaToAltitude converts hectopascals or millibars to altitude (meters)
  * @param hpa hectorpascals in millibars
  * @param temperature in kelvin (default=288.15)
  * @param msle mean sea level pressure (default=1013.25)
@@ -26,6 +26,48 @@ namespace radix
  */
 Real RADIX_PUBLIC hpaToAltitude(Real hpa, Real temperature = 288.15,
                                 Real msle = 1013.25);
+
+/**
+ * @brief absoluteTemperature Get the temperature of an air parcel given its
+ * potential temperature and pressure
+ * @param potentialTemp Potential temperature in Kelvin
+ * @param pressure Pressure in mb
+ * @return Absolute temperature (K)
+ */
+Real RADIX_PUBLIC absoluteTemperature(Real potentialTemp, Real pressure);
+
+/**
+ * @brief saturationVaporPressure Calculate the saturation pressure of an air
+ * parcel given its absolute temperature and pressure
+ * @param absTemp Absolute temperature in Kelvin
+ * @param pressure Pressure in mb
+ * @return Saturation vapour pressure (mb)
+ */
+Real RADIX_PUBLIC saturationVaporPressure(Real absTemp, Real pressure);
+
+/**
+ * @brief mixingRatioToRelativeHumidity Get the relative humidity of an air
+ * parcel given a mixing ratio, temperature and pressure
+ * @param mixingRatio Mixing ratio (g/g)
+ * @param absTemp Absolute temperature (K)
+ * @param pressure Pressure (mb)
+ * @return Relative humidity (%)
+ */
+Real RADIX_PUBLIC mixingRatioToRelativeHumidity(Real mixingRatio, Real absTemp,
+                                                Real pressure);
+
+/**
+ * @brief specificHumidityToRelativeHumidity Get the relative humidity of an air
+ * parcel given a specific humidity, temperature and pressure
+ * @param specificHumidity Specific humidity (g/kg)
+ * @param absTemp Absolute temperature (K)
+ * @param pressure Pressure (mb)
+ * @return Relative humidity (%)
+ */
+Real RADIX_PUBLIC specificHumidityToRelativeHumidity(Real specificHumidity,
+                                                     Real absTemp,
+                                                     Real pressure);
+
 /**
  * @brief cspanf returns a value in the interval (begin,end]
  * This function is used to reduce periodic variables to a standard range.