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Measurement campaign at Ruisdael Observatory

Currently, a measurement campaign is carried out at the Ruisdael Observatory. The campaign takes place at the measurement site in Cabauw and still runs until the 21st of May 2021. The goal of this campaign is to test and align measurement strategies of different instruments involved as preparation for a large Ruisdael campaign in the period August-September 2021. This large Ruisdael campaign more broadly targets collocated measurements of surface-atmosphere interactions through momentum and scalar (heat/moisture/chemical tracers) transport, aerosols, clouds and radiation.

In the current campaign a lot of instruments are collocated at the Cabauw site to address which measurement strategies best target the questions to be addressed in the larger Summer campaign. Ideal weather situations involve considerable wind and broken cloud (cumulus) regimes. During the first week, plenty of wind and broken cloud decks dominated over Cabauw and the Netherlands, with even some deep convective thunderstorms earlier in the week.

In this campaign, two NWO-funded Vidi projects Tracing Convective Momentum Transport in Complex Cloudy Atmospheres (CMTRACE, Nuijens) and Shedding Light on Cloud Shadows (SLOCS, van Heerwaarden) join forces to carry out new strategies. For CMTRACE, a new WindCube and two scanning cloud radars are measuring in an unconventional coordinated effort made possible with the help of Steven Knoop (KNMI), Christine Unal and Rob McKenzie (both TUD). For SLOCS, a horizontal grid of radiation measurements has been installed in the grass fields of Cabauw, thanks to the special efforts of PhD’s Wouter Mol (WUR) and Katherine Heimerl (VU) who coordinate the measurements and who can be found often on location (see the pictures).

Each of the two projects has its own objective. Doing the measurements at the same time has valuable benefits: high-resolution wind measurements at cloud level are valuable for SLOCS by providing information about the speed at which clouds move, which helps set the temporal scale of solar irradiance variability. Vice versa, solar irradiance measurements on a larger grid than just the straw-view of clouds at Cabauw helps CMTRACE to identify how cloud shading limits momentum transport through the mixed layer by reducing the surface buoyancy flux.

Furthermore, aerosol optical closure experiments and aerosol-cloud closure experiments are part of the Chinese Scholarship Council funded PhD project of Xinya Liu. The wind-field/cloud dynamics and microphysics observations of CMTRACE will help to link aerosol measurements to cloud microphysics.

All data will become available on the Ruisdael Data Archive, which will be centralized at the KNMI Data Platform (KDP).