Understanding and Calculating the Environmental Lapse Rate
The environmental lapse rate (ELR) is a fundamental concept in atmospheric science and meteorology. It describes the rate at which atmospheric temperature decreases with an increase in altitude. This rate is crucial for understanding weather patterns, cloud formation, atmospheric stability, and even the design of aviation and engineering projects. Unlike adiabatic lapse rates (which consider the temperature changes within a rising or sinking parcel of air), the environmental lapse rate measures the actual temperature change of the surrounding atmosphere.
The ELR is not constant and can vary significantly depending on geographical location, time of day, season, and weather conditions. Factors like solar radiation, cloud cover, and surface heating all influence how temperature changes with altitude.
### How to Calculate the Environmental Lapse Rate
To calculate the environmental lapse rate, you need two measurements: the temperature at a lower altitude and the temperature at a higher altitude. The formula is straightforward:
**Environmental Lapse Rate = (Temperature at Lower Altitude – Temperature at Higher Altitude) / (Higher Altitude – Lower Altitude)**
The result is typically expressed in degrees Celsius per 100 meters (°C/100m) or degrees Fahrenheit per 1000 feet (°F/1000ft).
**Formula in Code:**
`lapseRate = (temp1 – temp2) / (altitude2 – altitude1);`
### Example Calculation
Let's say you have the following measurements:
* **Lower Altitude (Altitude 1):** 500 meters
* **Temperature at Lower Altitude (Temp 1):** 20°C
* **Higher Altitude (Altitude 2):** 1500 meters
* **Temperature at Higher Altitude (Temp 2):** 10°C
Using the formula:
ELR = (20°C – 10°C) / (1500m – 500m)
ELR = 10°C / 1000m
ELR = 0.01°C/m
To express this in °C/100m:
ELR = 0.01°C/m * 100m = 1°C/100m
This means the temperature decreases by 1 degree Celsius for every 100 meters you ascend in this specific atmospheric condition.
Environmental Lapse Rate Calculator
function calculateLapseRate() {
var altitude1 = parseFloat(document.getElementById("altitude1").value);
var temperature1 = parseFloat(document.getElementById("temperature1").value);
var altitude2 = parseFloat(document.getElementById("altitude2").value);
var temperature2 = parseFloat(document.getElementById("temperature2").value);
var resultDiv = document.getElementById("result");
if (isNaN(altitude1) || isNaN(temperature1) || isNaN(altitude2) || isNaN(temperature2)) {
resultDiv.textContent = "Please enter valid numbers for all fields.";
return;
}
if (altitude1 === altitude2) {
resultDiv.textContent = "Lower and higher altitudes cannot be the same.";
return;
}
var altitudeDifference = altitude2 – altitude1;
var temperatureDifference = temperature1 – temperature2;
var lapseRatePerMeter = temperatureDifference / altitudeDifference;
// Standardize result to °C per 100 meters
var lapseRatePer100Meters = lapseRatePerMeter * 100;
// Standardize result to °F per 1000 feet
var altitudeDifferenceFeet = altitudeDifference * 3.28084; // meters to feet
var temperatureDifferenceFahrenheit = temperatureDifference * 1.8; // Celsius to Fahrenheit
var lapseRatePer1000Feet = (temperatureDifferenceFahrenheit / altitudeDifferenceFeet) * 1000;
resultDiv.innerHTML = "Environmental Lapse Rate: " +
lapseRatePer100Meters.toFixed(2) + " °C/100m " +
lapseRatePer1000Feet.toFixed(2) + " °F/1000ft";
}
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