Vaisala RS92 Research Articles

Temperature Error of the Vaisala RS90 Radiosonde

The new F-Thermocap sensor used on the Vaisala RS90 radiosonde is a miniaturized capacitive sensor designed to decrease the solar radiation error and the time lag error that exists with the Thermocap sensor used on the RS80 radiosonde. The heating and response characteristics of the F-Thermocap sensor were evaluated by developing a heat balance model, RS90COR, that calculates the temperature of the sensor relative to the air temperature in various flight environments. The temperature of the F-Thermocap sensor was found to be essentially identical to that of the atmosphere in all nighttime environments. In daytime conditions solar heating of the sensor increases its temperature to slightly above that of the ambient air. The daytime error increases with altitude but remains less than 0.5°C to an altitude of 35 km. The time lag error of the miniaturized sensor is insignificant. The RS90COR modeling results were validated by using model-predicted errors to correct RS90 and RS80 temperature profiles from sondes flown on the same balloon. The corrected profiles agreed, except for a temperature bias of 0.1°–0.3°C that results from a calibration or electronics error in one or both of the sondes. A new source of temperature error in daytime flights of RS80, RS90, and VIZ radiosondes has been discovered that relates to the orientation of the sensor with respect to the impinging solar radiation. This orientation error is smallest in the RS90 sensor.

On the use of radiosonde humidity observations in mid-latitude NWP

We compare radiosonde observations of relative humidity with NWP versions of the Meteorological Office Unified Model, and attempt to understand the causes of the systematic differences seen. The differences are found to have a different structure in cyclonic and anticyclonic situations over the UK. In cyclonic situations the mid-tropospheric temperature and humidity differences could be due to model biases, consistent with the conservation of energy; the latent heating from precipitation of the model's excess moisture would remove the model's cold bias. There is also some evidence for observational bias. Wetting of the sonde sensor in cloud can cause a moist bias at higher levels. The Vaisala RS80 sonde also appears to have a dry bias near saturation.

Temperature Corrections for the VIZ and Vaisala Radiosondes

The National Weather Service VIZ radiosonde and the Vaisala RS-80 radiosondes are used worldwide to obtain upper-air measurements of atmospheric temperature and moisture. The temperature measured by each sensor is not equal to the atmospheric temperature due to solar and infrared irradiation of the sensor, heat conduction to the sensor from its attachment points, and radiation emitted by the sensor. Presently, only the RS-80 radiosonde applies corrections to the sensor temperature to compensate for these heating sources, and this correction is only considered to be a function of solar angle and pressure. Temperature correction models VIZCOR (VIZ sonde) and VAICOR (Vaisala RS-80 sonde) have been developed that derive the atmospheric temperature from the sensor temperature, taking into account all significant environmental processes that influence the beat transfer to the sensor. These models have been validated by comparing their corrected profiles with atmospheric temperature profiles derived from the NASA multithermistor radiosonde. All three radiosondes were flown on the same balloon during the potential reference radiosonde intercomparison. Excellent agreement has been found between all profiles up to an altitude of 30 km. Since the significant error sources in the VIZCOR, VAICOR, and multithermistor techniques are largely independent, agreement between all profiles implies that the corrected sensor profiles are providing an unbiased estimate of the true atmospheric temperature.

A Comparison of Philips RS4 and Väisälä RS80 Radiosonde Data

Abstract The paper describes the results of an experiment where, for a series of flights, Philips RS4 and Vaisala RS80 radiosondes were mounted on the same balloon. It is shown that there are both random and systematic differences in the raw and derived data generated from these systems. At all levels above 1000 hPa, solar corrected RS4 temperature soundings are colder than those of the RS8O; resulting in a geopotential height difference of the order of 90 m at 50 hPa. The Vaisala RS8O Omega winds are similar to radar-derived wind profiles except in regions of changing vertical shear.