Skip to content
PilotSchool Knowledge Base

Measuring Surface Air Temperature and Its Implications

Introduction

In aviation meteorology, accurate measurement of surface air temperature at airfields is essential. It directly influences aircraft performance and the safety of operations during take-offs and landings. This section will cover methods for measuring surface air temperature and how these temperatures can relate to actual conditions above the runway.

Measurement of Surface Air Temperature

Standard Instruments Used

The measurement of surface air temperature at airfields employs various meteorological instruments. Key among these are:

  • Digital Current Weather Instrument System (DCWIS): This system includes a temperature-humidity sensor among other components such as wind direction and speed sensors and a barometric pressure sensor. The data is digitized and transmitted for analysis.

  • Temperature Measurement Instruments: These typically involve a temperature sensor, such as a Pt-100 RTD sensor, which operates by varying resistance in response to temperature changes. Its range is from -40°C to 60°C, with an output of 0-1 volts DC.

Criteria for Installation

Proper installation of meteorological equipment is crucial for accuracy. The site requirements include an area with free exposure conditions at an elevation similar to the runway. Temperature sensors are usually mounted on a 2-meter-high tubular mast within a Stevenson screen, ensuring that readings represent temperature conditions pertinent to take-offs and landings Overview of Aviation of Meteorological Instruments - IMD Pune.

Relating Surface Air Temperature to Runway Conditions

Localized Heating Effects

It is important to recognize that surface air temperatures measured in open areas can differ significantly from actual runway surface temperatures due to localized solar heating. While no specific calculations are adjusted for this effect, the inherent safety margins in aircraft performance tables account for variations like runway heating.

Adiabatic Lapse Rates

The adiabatic lapse rate describes the rate of temperature change with altitude. There are two main types:

  • Dry Adiabatic Lapse Rate (DALR): Approximately 3°C per 1000 feet for unsaturated air.
  • Saturated Adiabatic Lapse Rate (SALR): About 1.5°C per 1000 feet at lower altitudes and latitudes.

Understanding these lapse rates assists pilots in interpreting weather conditions and their potential impact on landing and takeoff performance Lapse Rate - SKYbrary.

Impact on Runway Surface Conditions

Geographic and Weather Conditions

Specific local conditions, such as dew or frost formation, can affect runway friction. These are typically identified using temperature and dew point spreads, often reported in METARs (Meteorological Terminal Aviation Routine Weather Reports). Such conditions underscore the importance of understanding micrometeorology and its potential impact on runway conditions Valuable Intelligence - Flight Safety Foundation.

Safety Margins and Operational Considerations

While specific procedures for adjusting aircraft performance based on runway surface temperatures are not standard, built-in safety margins cover factors such as solar heating and reduced friction due to weather conditions. Additionally, METAR data aids in early identification of runway threats that could impact performance.

Conclusion

Accurate measurement of surface air temperature and a robust understanding of local meteorological effects and adiabatic lapse rates are crucial in aviation operations. These elements help ensure safe and efficient flight patterns, particularly during critical phases of take-off and landing. Understanding the interplay between airfield and runway temperatures, informed by reliable measurements and applicable meteorological knowledge, supports effective flight planning and enhances operational safety.