Abstract
Abstract. Accurate measurements of temperature and water vapor in the upper-air are of great interest in relation to weather prediction and climate change. Those measurements are mostly conducted using radiosondes equipped with a variety of sensors that are flown by a balloon up to lower stratosphere. Reference Upper Air Network (GRUAN) has identified water vapor pressure as one of the most important measurands and has set an accuracy requirement of 2 % in terms of the mixing ratio. In order to achieve the requirement, many errors in the humidity measurement such as a temperature dependency in sensing characteristics including measurement values and response time need to be corrected because humidity sensors of radiosondes pass through low-pressure (1 kPa) and low-temperature (−80 ∘C) environments in the upper-air. In this paper, the humidity sensing characteristics of Jinyang radiosonde sensors in relation to temperature dependencies were evaluated at low temperature using a newly developed ultralow-temperature humidity chamber. The sensitivity characteristic curve of the radiosonde sensors was evaluated down to −80 ∘C, and the calibration curves of the humidity sensor and the temperature sensor were obtained. The response time of humidity sensor slowly increased from 52 to 116 s at the temperature from 20 to −40 ∘C, respectively, and then rapidly increased to almost one hour at −80 ∘C. Those results will help to improve the reliability of the upper-air observation data.
Highlights
The measurement of upper-air temperature and humidity plays an important role in various fields, e.g., addressing global warming, forecasting weather, and ensuring aviation safety
Radiosonde sensor characteristics were evaluated with the ultralow-temperature humidity chamber (UTHC)
The evaluation of humidity sensors was carried out as follows: the humidity sensors were first calibrated at room temperature (20 ◦C); the temperature of the test chamber was decreased to −80 ◦C; and the temperature was in
Summary
The measurement of upper-air temperature and humidity plays an important role in various fields, e.g., addressing global warming, forecasting weather, and ensuring aviation safety. It is necessary to evaluate radiosonde sensors using an ultralow-temperature humidity chamber (UTHC) which enables more reliable measurements as well as the traceability of measurements to the upper air conditions. According to the measurement standards set by the WMO’s Reference Upper Air Network (GRUAN), the uncertainty of measurement is specified for temperature and humidity measurement and for wind speed and pressure measurement These efforts show that the global trend in meteorological measurements is moving towards improving reliability. Its UTHC was based on a hybrid humidity generator principle (Mayer et al, 2008), in which the carrier gas passing through a saturator and a zero gas supplier mixed in a controlled way for the humidity generation In this regard, it allows a fast humidity change by controlling the mixing ratio and can be useful for studying dynamic responses of humidity sensors in addition to the calibration at static states. A more detailed description on UTHC is being prepared as an independent paper
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