Question about temperature measurements

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SUMMARY

This discussion centers on the accuracy of temperature measurements, specifically distinguishing between shade temperatures and those taken under direct sunlight. Shade temperatures, measured in ventilated white shelters known as Stevenson Screens, are consistently lower than direct sunlight readings, which reflect the thermometer's temperature rather than the air temperature. Official measurements are taken at 1.5 meters above ground, and while there is no specified ventilation rate for these shelters, forced ventilation options exist but are rarely used. The discussion highlights the importance of understanding the conditions under which temperature data is collected, as meteorological temperatures are influenced by both true air temperature and wind speed.

PREREQUISITES
  • Understanding of Stevenson Screens and their role in meteorological measurements
  • Knowledge of albedo and its effect on temperature readings
  • Familiarity with the concept of ventilation in temperature measurement
  • Basic principles of meteorology, including the impact of wind speed on temperature
NEXT STEPS
  • Research the design and specifications of Stevenson Screens for accurate temperature measurement
  • Explore the effects of albedo on temperature readings in different environments
  • Investigate the role of forced ventilation in meteorological shelters and its impact on data accuracy
  • Learn about the relationship between wind speed and meteorological temperature readings
USEFUL FOR

Meteorologists, environmental scientists, and anyone involved in climate data collection and analysis will benefit from this discussion.

Simfish
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Used in measured highs/lows/hourly temperatures.

Are they shade temperatures or temperatures under the Sun? Also - are shade temperatures really cooler than temperatures under the Sun?
 
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Yes, they are shade temperatures, and yes, these are often much lower than a reading under direct sunlight. A temperature measurement under direct sunlight will only tell you the temperature of the thermometer itself, not the air temperature.
 
http://www.rickly.com/MI/InstrumentShelter.htm
 
Last edited by a moderator:
When I was in high school, they used to call those things Stevenson Screens.
 
All official measurements are taken about 1.5 meters above the ground, in a white shelter that is ventilated at a certain rate. The white color (ideally) gives the shelter a very high albedo, close to 100%, which means that it won't absorb sunlight and warm up... the ventilation keeps the air mixed and fresh (think greenhouse effect, or lack thereof).

Unfortunately, this can lead to problems... you can imagine that shelters don't stay perfectly white throughout their existence, for instance.
 
Weather Freak said:
All official measurements are taken about 1.5 meters above the ground, in a white shelter that is ventilated at a certain rate.

What rate is that? When was such a specification added? How are "corrections" made for "unventilated" data collected prior to that time?

For the record, there is no ventilation rate specified; there are forced ventilation shelters available, but they are not in common use.

The white color (ideally) gives the shelter a very high albedo, close to 100%, which means that it won't absorb sunlight and warm up... the ventilation keeps the air mixed and fresh (think greenhouse effect, or lack thereof).

"100%?" "Certain conditions and restrictions apply. Substantial penalties for early withdrawal, or in other random events." This is for chalk, clay, lead, or titanium whites? Oil, resin, lacquer, enamel, or latex bases? 5800 K emissivities run 0.1 - 0.3; 300 K emissivities run 0.6 - 0.8; temperature rises can get to 5 - 10 K in still air.

Unfortunately, this can lead to problems... you can imagine that shelters don't stay perfectly white throughout their existence, for instance.

Meteorological temperatures are NOT true air temperatures; they are a combination of true air temperature and wind speed.
 

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