## Description *Shedding Light On Cloud Shadows (SLOCS)* is a project funded by the [NWO VIDI](https://www.nwo.nl/en/researchprogrammes/nwo-talentprogramme/projects-vidi/2018) scheme. The main aim of SLOCS is to understand the variability in incoming solar radiation due to clouds, and to find physically accurate, yet fast, methods for simulating the variability. SLOCS will make heavily use of the new [Ruisdael Observatory](http://ruisdael-observatory.nl/), as we will roll out a grid of radiation measurement devices surrounding the Cabauw measurement tower in collaboration with the [KNMI](https://www.knmi.nl/), and we will participate in international field campaigns, such as [FESSTVaL](https://fesstval.de/en/) and [LIAISE](https://www.hymex.fr/liaise/index.html). ![[ruisdael_haarlem.jpg]] *Patterns of light and shadows created by clouds with Haarlem in the background as painted by Ruisdael in the 17th century. Source: [Wikipedia](https://en.wikipedia.org/wiki/List_of_paintings_by_Jacob_van_Ruisdael)* We will **i)** observe the variability at unprecedented spatial, temporal, and spectral resolution, **ii)** use our GPU-enabled virtual laboratory [MicroHH](https://microhh.org) to develop computationally affordable simulation techniques that capture the observed variability, and **iii)** validate the newly developed techniques in realistic cloud-resolving simulations, to ensure that the acquired knowledge becomes available to the weather forecasting and solar energy fields. In the last step, we will make use of the Ruisdael Testbed for large-eddy simulations to compare simulations against observational data, and we will collaborate with [Whiffle](http://www.whiffle.nl/), who kindly provided an in-kind contribution to SLOCS in the form of simulation data. ## Output - In [[Publications#^Mol2024|Observed patterns of surface solar irradiance under cloudy and clear-sky conditions]] we present the results of the analysis of our field observations of surface solar irradiance of the [FESSTVaL](https://fesstval.de/en/) and [LIAISE](https://www.hymex.fr/liaise/index.html) field campaigns and present the characteristics of cloud shadows and enhancements for cumulus, altocumulus, and cirrus clouds and show the large differences among those, including an analysis of light color variations in and around shadows. ^output-Mol2024 - In *[[Publications#^Veerman2024|The impact of radiative transfer at reduced spectral resolution in large-eddy simulations of convective clouds (2024)]]* we study how much spectral detail we can drop in radiative transfer computations before the quality of cloud-resolving simulations drops. We show that it is possible to reduce the resolution a factor 3-4 compared to standard computations without significant loss of quality. - In *[[Publications#^Mol2023-essd|Ten years of 1 Hz solar irradiance observations at Cabauw, the Netherlands, with cloud observations, variability classifications, and statistics (2023).]]* we present a dataset with 10 years of 1 Hz surface solar irradiance observations at Cabauw, The Netherlands, bundled with cloud observations and a classification of the conditions into direct sunlight, shadows, and cloud enhancements. - We have developed [(LS)<sup>2</sup>D](https://github.com/LS2D) a Python package to generate initial conditions and boundary conditions from ERA5 for realistic doubly-periodic large-eddy simulations. In the paper *[[Publications#^vanStratum2023|The benefits and challenges of downscaling a global reanalysis with doubly‐periodic large‐eddy simulations (2023)]]* we demonstrate the tool at the location of the Cabauw measurement site and show the impact of grid resolution and domain size on surface solar irradiance variability. - In *[[Publications#^Mol2023-jgr|Reconciling observations of solar irradiance variability with cloud size distributions (2023)]]* we use the dataset above to demonstrate the presence of power laws in surface solar irradiance observations. - We have developed FROST, a cheap radiation measurement device that can measure incoming shortwave radiation with 10 Hz at multiple spectra bands ranging from UV to near-infrared. FROST is presented in *[[Publications#^Heusinkveld2023|A new accurate low-cost instrument for fast synchronized spatial measurements of light spectra (2023)]]*. - By coupling our newly developed GPU ray tracer to [[MicroHH]], we demonstrate that in a case study for a cumulus day in Cabauw, The Netherlands that simulations with 3D radiation produce deeper and larger clouds than simulations with 1D radiation (the status quo). Read more in *[[Publications#^Veerman2022|A case study of cumulus convection over land in cloud‐resolving simulations with a coupled ray tracer]]*. Watch the movie below to see cloud enhancements (red color, more surface solar irradiance than under a blue sky) in between cloud shadows. <div style="padding:52.6% 0 0 0;position:relative;"><iframe src="https://player.vimeo.com/video/737842440?h=ae0ee92bce&loop=1&title=0&byline=0&portrait=0" style="position:absolute;top:0;left:0;width:100%;height:100%;" frameborder="0" allow="autoplay; fullscreen; picture-in-picture" allowfullscreen></iframe></div><script src="https://player.vimeo.com/api/player.js"></script> - In *[[Publications#^vanHeerwaarden2021|Record high solar irradiance during first COVID-19 lockdown largely due to unusual weather (2021)]]* we explain why we measured so much surface solar irradiance during the first COVID-19 lockdown. It turned out, it had little to do with less pollution, and instead it was driven by very unusual weather leading to much brighter skies than in typical Western-European spring.