iMS-100 GRUAN Data Product Version 2 (IMS-100-GDP.2)

This dataset comprises reference radiosoundings performed with the Meisei iMS-100. Reference, in this case, means that: all known biases are corrected for, best possible vertically resolved uncertainty estimates, well-documented correction algorithms, extensive metadata collection. The GCOS (Global Climate Observing System) Reference Upper-Air Network (GRUAN) data processing for the Meisei iMS-100 radiosonde was developed to meet the criteria for reference measurements. These criteria stipulate the collection of metadata, the use of well-documented correction algorithms, and estimates of the measurement uncertainty. An important and novel aspect of the GRUAN processing is that the uncertainty estimates are vertically resolved. The algorithms that are applied in version 2 of the GRUAN processing to correct for systematic errors in radiosonde measurements of pressure, temperature, humidity, and wind, as well as how the uncertainties related to these error sources are derived. The iMS-100 was regularly launched at Tateno (TAT) and Minamitorishima (MTS) since September 2017. It has also been regularly launched at Singapore (SNG) since 2021. An additional GRUAN requirement for performing reference measurements with the iMS-100 is that the manufacturer-prescribed procedure with the indoor environment for the radiosonde's preparation and the supplementary procedure with the Standard Humidity Chamber (SHC) at 0 %RH and 100 %RH environment are followed. The reference measurements with SHC are applied for the recalibration of the humidity sensors. For the dominant error source, solar radiation, laboratory experiments were performed to investigate and model its effect on the iMS-100's temperature and humidity measurements. GRUAN uncertainty (k=1) estimates are 0.4 K for night-time temperature measurements and approximately 0.8 K at 25 km during daytime. The other uncertainty estimates are up to 7 %RH for humidity, 20 m for geopotential height, 1.2 hPa for pressure, 1.5 m/s for wind speed, and 1° for wind direction. Intercomparison measurements with Vaisala RS92-GDP show that the temperature of IMS-100-GDP is 0.5 K lower than RS92-GDP in the stratosphere at daytime. The relative humidity measurements of IMS-100-GDP are about 2 %RH larger than RS92-GDP in the lower troposphere (below 500 hPa level) and less than 5 %RH in the middle and upper troposphere. Intercomparison measurements with the chilled-mirror hygrometer, Meisei SKYDEW (Sugidachi, 2019), iMS-100 show ±5 %RH difference from the SKYDEW.