Abstract

<strong class="journal-contentHeaderColor">Abstract.</strong> Radiosonde descent profiles have been available from tens of stations for several years now – mainly from Vaisala RS41 radiosondes. They have been compared with the ascent profiles, with ECMWF short-range forecasts and with co-located radio occultation retrievals. Over this time, our understanding of the data has grown, and the comparison has also shed some light on radiosonde ascent data. The fall rate is very variable and is an important factor, with high fall rates being associated with temperature biases, especially at higher altitudes. Ascent winds are affected by pendulum motion; on average, descent winds are less affected by pendulum motion and are smoother. It is plausible that the true wind variability in the vertical lies between that shown by ascent and descent profiles. This discrepancy indicates the need for reference wind measurements. With current processing, the best results are for radiosondes with parachutes and pressure sensors. Some of the wind, temperature and humidity data are now assimilated in the ECMWF forecast system.

Highlights

  • Radiosondes were first developed in the 1930s and have been used to measure profiles of temperature, humidity and wind since

  • A smaller version of the same effect can be seen between the German data and the UK data; the latter data have an offset of about 0.1 ◦C in the troposphere, which is smaller than the Finnish offset because the UK radiosondes have parachutes

  • 6 Discussion and conclusions The most obvious difference between ascent and descent data is that the descent temperatures are higher at upper levels

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Summary

Introduction

Radiosondes were first developed in the 1930s and have been used to measure profiles of temperature, humidity and wind since . Tiefenau and Gebbeken (1989) compared ascent and descent temperatures and found the descent values to be higher at upper levels. (2021) found that 44 % of operational radiosonde stations were providing high-vertical-resolution ascent data in mid-2020. Ing in the radio signal to the launch station being lost at higher altitudes on descent due to obstruction by terrain or signal attenuation. This can be seen clearly in the UK results which have been split into automatic and manual launches: the manual launches use larger balloons, and the number of descent reports starts to decline earlier (below 9 km). Usually less than 5 %, do not have a corresponding descent report, often due to a fault developing with the radiosonde before or upon burst, leading to an automatic termination

What goes up must come down
Types of parachute and string length
Preparation of profile reports
Descent fall rates
Motion of radiosonde during descent
The ECMWF forecasting system
Wind comparison
Temperature comparison
Humidity comparison
The direct effect of heating
The indirect effect of heating
Assimilation of descent data
Findings
Discussion and conclusions

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