Environmental Lapse Rate Calculator

by
Environmental Lapse Rate Calculator .elr-calculator-container { font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif; max-width: 800px; margin: 0 auto; padding: 20px; background-color: #f9fbfd; border: 1px solid #e1e4e8; border-radius: 8px; } .elr-header { text-align: center; margin-bottom: 30px; } .elr-header h2 { color: #2c3e50; margin-bottom: 10px; } .elr-grid { display: grid; grid-template-columns: 1fr 1fr; gap: 20px; margin-bottom: 20px; } @media (max-width: 600px) { .elr-grid { grid-template-columns: 1fr; } } .elr-input-group { margin-bottom: 15px; } .elr-input-group label { display: block; font-weight: 600; margin-bottom: 5px; color: #4a5568; } .elr-input-group input, .elr-input-group select { width: 100%; padding: 10px; border: 1px solid #cbd5e0; border-radius: 4px; font-size: 16px; box-sizing: border-box; } .elr-input-group input:focus { border-color: #3182ce; outline: none; box-shadow: 0 0 0 3px rgba(49, 130, 206, 0.1); } .elr-btn { width: 100%; padding: 12px; background-color: #3182ce; color: white; border: none; border-radius: 4px; font-size: 18px; font-weight: bold; cursor: pointer; transition: background-color 0.2s; } .elr-btn:hover { background-color: #2b6cb0; } .elr-result { margin-top: 25px; padding: 20px; background-color: #fff; border: 1px solid #e2e8f0; border-radius: 6px; display: none; } .elr-result-value { font-size: 32px; font-weight: bold; color: #2d3748; text-align: center; margin-bottom: 10px; } .elr-result-label { text-align: center; color: #718096; font-size: 14px; text-transform: uppercase; letter-spacing: 1px; } .elr-stability-box { margin-top: 15px; padding: 10px; text-align: center; border-radius: 4px; font-weight: bold; } .elr-content { margin-top: 40px; line-height: 1.6; color: #2d3748; } .elr-content h3 { color: #2c3e50; margin-top: 25px; } .elr-content p { margin-bottom: 15px; } .elr-content ul { margin-bottom: 15px; padding-left: 20px; } .elr-content li { margin-bottom: 8px; } .note { font-size: 0.9em; color: #666; font-style: italic; } function updateLabels() { var unit = document.getElementById('elr_unit').value; var altLabels = document.getElementsByClassName('label-alt'); var tempLabels = document.getElementsByClassName('label-temp'); if (unit === 'metric') { for(var i=0; i<altLabels.length; i++) altLabels[i].innerText = "Altitude (Meters)"; for(var i=0; i<tempLabels.length; i++) tempLabels[i].innerText = "Temperature (°C)"; } else { for(var i=0; i<altLabels.length; i++) altLabels[i].innerText = "Altitude (Feet)"; for(var i=0; i Z1 (going up), and T2 < T1 (getting colder), result is positive lapse rate. var tempDiff = temp1 – temp2; // Drop in temperature var altDiff = alt2 – alt1; // Change in height // Handle negative altitude difference if user swapped inputs if (altDiff < 0) { altDiff = alt1 – alt2; tempDiff = temp2 – temp1; } // 3. Calculation var lapseRate = 0; var resultText = ""; var stabilityText = ""; var stabilityColor = "#e2e8f0"; var stabilityTextColor = "#2d3748"; if (unit === 'metric') { // Result in °C/km // altDiff is in meters, convert to km var altDiffKm = altDiff / 1000; lapseRate = tempDiff / altDiffKm; resultText = lapseRate.toFixed(2) + " °C/km"; // Stability Logic (Metric) // DALR approx 9.8 C/km, SALR approx 6.0 C/km if (lapseRate < 0) { stabilityText = "Temperature Inversion (Very Stable)"; stabilityColor = "#48bb78"; // Green stabilityTextColor = "#fff"; } else if (lapseRate = 6.0 && lapseRate < 9.8) { stabilityText = "Conditionally Unstable"; stabilityColor = "#ecc94b"; // Yellow } else { stabilityText = "Absolutely Unstable"; stabilityColor = "#f56565"; // Red stabilityTextColor = "#fff"; } } else { // Result in °F/1000ft // altDiff is in feet, normalize to 1000ft units var altDiffThou = altDiff / 1000; lapseRate = tempDiff / altDiffThou; resultText = lapseRate.toFixed(2) + " °F/1,000 ft"; // Stability Logic (Imperial) // DALR approx 5.4 F/1000ft, SALR approx 3.3 F/1000ft if (lapseRate < 0) { stabilityText = "Temperature Inversion (Very Stable)"; stabilityColor = "#48bb78"; stabilityTextColor = "#fff"; } else if (lapseRate = 3.3 && lapseRate < 5.4) { stabilityText = "Conditionally Unstable"; stabilityColor = "#ecc94b"; } else { stabilityText = "Absolutely Unstable"; stabilityColor = "#f56565"; stabilityTextColor = "#fff"; } } // 4. Output var resultDiv = document.getElementById('elr_result_container'); var resultValDiv = document.getElementById('elr_result_val'); var stabilityDiv = document.getElementById('elr_stability_msg'); resultDiv.style.display = "block"; resultValDiv.innerHTML = resultText; stabilityDiv.innerHTML = stabilityText; stabilityDiv.style.backgroundColor = stabilityColor; stabilityDiv.style.color = stabilityTextColor; }

Environmental Lapse Rate Calculator

Calculate the vertical temperature gradient of the atmosphere.

Metric (Meters, °C) Imperial (Feet, °F)

Lower Elevation Point

Higher Elevation Point

Calculated Lapse Rate

Positive values indicate temperature decreases with height (Normal). Negative values indicate an Inversion.

What is Environmental Lapse Rate (ELR)?

The Environmental Lapse Rate (ELR) refers to the actual rate at which the ambient temperature of the atmosphere decreases with an increase in altitude. Unlike theoretical adiabatic rates, the ELR represents the specific conditions of the atmosphere at a given place and time, which is usually measured using weather balloons (radiosondes).

How to Calculate Lapse Rate

The formula to calculate the Environmental Lapse Rate is relatively straightforward. It calculates the change in temperature divided by the change in altitude.

ELR = -(T2 – T1) / (Z2 – Z1)

  • T1, T2: Temperature at the lower and higher altitudes, respectively.
  • Z1, Z2: The height of the lower and higher altitudes.

Typically, temperature drops as you go higher. A standard "normal" lapse rate is often cited as 6.5°C per kilometer (or roughly 3.5°F per 1,000 ft).

Understanding Atmospheric Stability

This calculator also determines the stability of the atmosphere by comparing your ELR against the Dry Adiabatic Lapse Rate (DALR) and the Saturated Adiabatic Lapse Rate (SALR).

1. Absolutely Unstable

If the ELR > DALR (approx 9.8°C/km), the air parcel rising will always be warmer than the surrounding air, causing it to continue rising rapidly. This leads to thunderstorms and turbulence.

2. Conditionally Unstable

If the SALR < ELR < DALR, the atmosphere is stable if the air is dry but unstable if the air becomes saturated (forms clouds). This is a very common state in the atmosphere.

3. Absolutely Stable

If the ELR < SALR (approx 6.0°C/km or lower), a rising air parcel will quickly become cooler than the surrounding air and sink back down. This suppresses cloud formation and leads to calm weather.

4. Temperature Inversion

If the ELR is negative, it means the temperature increases with height. This creates a "lid" on the atmosphere, trapping pollutants, fog, and smoke near the ground.

Leave a Comment