Pyranometer offsets triggered by ambient meteorology: insights from laboratory and field experiments

Sandro M. Oswald, Helga Pietsch, Dietmar J. Baumgartner, Philipp Weihs, Harald E. Rieder
2017 Atmospheric Measurement Techniques  
<p><strong>Abstract.</strong> This study investigates the effects of ambient meteorology on the accuracy of radiation (<i>R</i>) measurements performed with pyranometers contained in various heating and ventilation systems (HV-systems). It focuses particularly on instrument offsets observed following precipitation events. To quantify pyranometer responses to precipitation, a series of controlled laboratory experiments as well as two targeted field campaigns were performed in 2016. The results
more » ... dicate that precipitation (as simulated by spray tests or observed under ambient conditions) significantly affects the thermal environment of the instruments and thus their stability. Statistical analyses of laboratory experiments showed that precipitation triggers zero offsets of −4<span class="thinspace"></span>W m<sup>−2</sup> or more, independent of the HV-system. Similar offsets were observed in field experiments under ambient environmental conditions, indicating a clear exceedance of BSRN (Baseline Surface Radiation Network) targets following precipitation events. All pyranometers required substantial time to return to their initial signal states after the simulated precipitation events. Therefore, for BSRN-class measurements, the recommendation would be to flag the radiation measurements during a natural precipitation event and 90<span class="thinspace"></span>min after it in nighttime conditions. Further daytime experiments show pyranometer offsets of 50<span class="thinspace"></span>W m<sup>−2</sup> or more in comparison to the reference system. As they show a substantially faster recovery, the recommendation would be to flag the radiation measurements within a natural precipitation event and 10<span class="thinspace"></span>min after it in daytime conditions.</p>
doi:10.5194/amt-10-1169-2017 fatcat:mzfouuxjczdrnepp2n2bhzlcae