function weather_format_apparent_temperature in Weather 7

Calculates apparent temperature.

This might be windchill (if cold and windy) or heat index (if hot and humid).

Windchill temperature is only defined for temperatures at or below 10 °C (50 °F) and wind speeds above 4.8 km/h (3 mph). Bright sunshine may increase the wind chill temperature. @link http://en.wikipedia.org/wiki/Wind_chill

The heat index is only defined for temperatures at or above 26.7 °C (80 °F) and a relative humidity above 40%. @link http://en.wikipedia.org/wiki/Heat_index

Parameters

int $metar: Structure with necessary information.

string $unit: Unit to be returned (celsius, fahrenheit, ...).

Return value

string Formatted representation in the desired unit. If the windchill is not defined for the current conditions, returns NULL.

1 call to weather_format_apparent_temperature()

theme_weather_theming in ./weather_theme.inc

Custom theme function for preprocessing the weather display.

File

./weather_theme.inc, line 241

Prepare themed weather output.

Code

function weather_format_apparent_temperature($metar, $unit) {

  // Set up the empty result, if apparent temperature is not defined
  // for current conditions.
  $result = NULL;

  // First, check conditions for windchill temperature.
  if ($metar->temperature <= 10) {
    if (isset($metar->wind_speed) and $metar->wind_speed >= 4.8) {

      // Calculate windchill (in degree Celsius).
      $windchill = round(13.12 + 0.6215000000000001 * $metar->temperature - 11.37 * pow($metar->wind_speed, 0.16) + 0.3965 * $metar->temperature * pow($metar->wind_speed, 0.16), 1);
      $result = weather_format_temperature($windchill, $unit);
    }
  }

  // Second, check conditions for heat index.
  if ($metar->temperature >= 26.7) {
    if (isset($metar->dewpoint)) {

      // Calculate relative humidity
      $e = 6.11 * pow(10, 7.5 * $metar->dewpoint / (237.7 + $metar->dewpoint));
      $es = 6.11 * pow(10, 7.5 * $metar->temperature / (237.7 + $metar->temperature));
      $h = max(0, min(100, round(100 * ($e / $es), 0)));
      if ($h >= 40) {

        // Calculate heat index (in degree Celsius).
        $c1 = -8.784694999999999;
        $c2 = 1.61139411;
        $c3 = 2.338549;
        $c4 = -0.14611605;
        $c5 = -0.012308094;
        $c6 = -0.016424828;
        $c7 = 0.002211732;
        $c8 = 0.00072546;
        $c9 = -3.582E-6;
        $t = $metar->temperature;
        $heatindex = round($c1 + $c2 * $t + $c3 * $h + $c4 * $t * $h + $c5 * $t * $t + $c6 * $h * $h + $c7 * $t * $t * $h + $c8 * $t * $h * $h + $c9 * $t * $t * $h * $h, 1);
        $result = weather_format_temperature($heatindex, $unit);
      }
    }
  }
  return $result;
}