Abstract
Abstract. Microwave radiometry is a suitable technique to measure atmospheric temperature profiles with high temporal resolution during clear sky and cloudy conditions. In this study, we included cloud models in the inversion algorithm of the microwave radiometer TEMPERA (TEMPErature RAdiometer) to determine the effect of cloud liquid water on the temperature retrievals. The cloud models were built based on measurements of cloud base altitude and integrated liquid water (ILW), all performed at the aerological station (MeteoSwiss) in Payerne (Switzerland). Cloud base altitudes were detected using ceilometer measurements while the ILW was measured by a HATPRO (Humidity And Temperature PROfiler) radiometer. To assess the quality of the TEMPERA retrieval when clouds were considered, the resulting temperature profiles were compared to 2 years of radiosonde measurements. The TEMPERA instrument measures radiation at 12 channels in the frequency range from 51 to 57 GHz, corresponding to the left wing of the oxygen emission line complex. When the full spectral information with all the 12 frequency channels was used, we found a marked improvement in the temperature retrievals after including a cloud model. The chosen cloud model influenced the resulting temperature profile, especially for high clouds and clouds with a large amount of liquid water. Using all 12 channels, however, presented large deviations between different cases, suggesting that additional uncertainties exist in the lower, more transparent channels. Using less spectral information with the higher, more opaque channels only also improved the temperature profiles when clouds where included, but the influence of the chosen cloud model was less important. We conclude that tropospheric temperature profiles can be optimized by considering clouds in the microwave retrieval, and that the choice of the cloud model has a direct impact on the resulting temperature profile.
Highlights
Measurements of tropospheric temperature with a high temporal resolution are fundamental for climate and weather research, to investigate atmospheric changes and to study dynamic or radiative processes in the atmosphere
The present study extends the work from NavasGuzmán et al (2014) by further investigating the influence of liquid water on temperature retrievals and by comparing tropospheric temperature profiles with radiosonde measurements at the same location
Our goal was to evaluate the effect of cloud liquid water on tropospheric temperature retrievals from a microwave radiometer
Summary
Measurements of tropospheric temperature with a high temporal resolution are fundamental for climate and weather research, to investigate atmospheric changes and to study dynamic or radiative processes in the atmosphere. Groundbased microwave radiometry has been discussed to be a suitable technique to provide continuous temperature measurements with a high temporal resolution (Askne and Westwater, 1986; Solheim et al, 1998; Crewell et al, 2001). Microwave radiometry has the advantage of being able to measure temperature during clear sky and cloudy weather conditions in contrast to other ground-based remote sensing techniques such as lidars or infrared spectrometers. This is due to the semitransparent properties of clouds in the microwave spectra (Löhnert et al, 2004). Liquid water in clouds still absorbs microwave radiation at some frequencies (Rosenkranz et al, 1972) and should be considered in the temperature retrievals
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