Shortwave surface radiation network for observing small-scale cloud inhomogeneity fields

Madhavan, Bomidi Lakshmi; Kalisch, John; Macke, Andreas

doi:10.5194/amt-9-1153-2016

Cited by 34 publications

(46 citation statements)

References 27 publications

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“…The temporal evolution of such shadow maps is calculated from cloud motion vectors that were calculated from subsequent sky images. Irradiance forecasts of up to 25 min have been produced and were validated against the network of pyranometers described in Madhavan et al (2016). Although these sky-imager-based forecasts do not outperform a simple persistence forecast on average, improved forecast skill was found for convective cloud conditions with high cloud and irradiance variability.…”

Section: Near-surface Wind Field and Energy Budgetmentioning

confidence: 99%

“…Based on the autonomous pyranometer network described in Madhavan et al (2016), the representativeness of a single station measurement for spatially extended domains with different area sizes has been investigated (Madhavan et al, 2017). This is an important aspect for the evaluation of model results with observations, where point measurements are mostly compared to grid-box means and are thus implicitly assumed to have similar statistical properties.…”

Section: Near-surface Wind Field and Energy Budgetmentioning

confidence: 99%

“…The pyranometer network (PYR) of 99 autonomous meteorological stations including pyranometers developed by TROPOS (Madhavan et al, 2016) was deployed within a radius of about 5 km around the supersite JUE to capture the broadband downwelling solar irradiance with high spatial and temporal resolution.…”

Section: Network Deployed In the Hope-jülich Areamentioning

confidence: 99%

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The HD(CP)<sup>2</sup> Observational Prototype Experiment (HOPE) – an overview

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Abstract. The HD(CP) 2 Observational Prototype Experiment (HOPE) was performed as a major 2-month field experiment in Jülich, Germany, in April and May 2013, followed by a smaller campaign in Melpitz, Germany, in September 2013. HOPE has been designed to provide an observational dataset for a critical evaluation of the new German community atmospheric icosahedral non-hydrostatic (ICON) model at the scale of the model simulations and further to provide information on land-surface-atmospheric boundary layer exchange, cloud and precipitation processes, as well as sub-grid variability and microphysical properties that are subject to parameterizations. HOPE focuses on the onset of clouds and precipitation in the convective atmospheric boundary layer. This paper summarizes the instrument set-ups, the intensive observation periods, and example results from both campaigns.HOPE-Jülich instrumentation included a radio sounding station, 4 Doppler lidars, 4 Raman lidars (3 of them providePublished by Copernicus Publications on behalf of the European Geosciences Union. temperature, 3 of them water vapour, and all of them particle backscatter data), 1 water vapour differential absorption lidar, 3 cloud radars, 5 microwave radiometers, 3 rain radars, 6 sky imagers, 99 pyranometers, and 5 sun photometers operated at different sites, some of them in synergy. The HOPEMelpitz campaign combined ground-based remote sensing of aerosols and clouds with helicopter-and balloon-based in situ observations in the atmospheric column and at the surface.HOPE provided an unprecedented collection of atmospheric dynamical, thermodynamical, and micro-and macrophysical properties of aerosols, clouds, and precipitation with high spatial and temporal resolution within a cube of approximately 10 × 10 × 10 km 3 . HOPE data will significantly contribute to our understanding of boundary layer dynamics and the formation of clouds and precipitation. The datasets have been made available through a dedicated data portal.First applications of HOPE data for model evaluation have shown a general agreement between observed and modelled boundary layer height, turbulence characteristics, and cloud coverage, but they also point to significant differences that deserve further investigations from both the observational and the modelling perspective.

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Section: Near-surface Wind Field and Energy Budgetmentioning

confidence: 99%

Section: Near-surface Wind Field and Energy Budgetmentioning

confidence: 99%

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The HD(CP)<sup>2</sup> Observational Prototype Experiment (HOPE) – an overview

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“…At the same time, the limited durations of the campaigns result in a data set that extends from mid-spring to mid-autumn, and may not be representative of other times of the year. Schmidt et al (2016) use data from the Jülich campaign for a performance evaluation of sky-imager-based solar irradiance forecasts, and Madhavan et al (2016) present a more detailed discussion of the campaign and the instrumentation. To the best of the authors' knowledge, no other PV-related studies based on comparably dense and high-frequency irradiance sensor networks have been published to date.…”

Section: Measurement Campaignsmentioning

confidence: 99%

Local short-term variability in solar irradiance

2016

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Abstract. Characterizing spatiotemporal irradiance variability is important for the successful grid integration of increasing numbers of photovoltaic (PV) power systems. Using 1 Hz data recorded by as many as 99 pyranometers during the HD(CP) 2 Observational Prototype Experiment (HOPE), we analyze field variability of clear-sky index k * (i.e., irradiance normalized to clear-sky conditions) and sub-minute k * increments (i.e., changes over specified intervals of time) for distances between tens of meters and about 10 km. By means of a simple classification scheme based on k * statistics, we identify overcast, clear, and mixed sky conditions, and demonstrate that the last of these is the most potentially problematic in terms of short-term PV power fluctuations. Under mixed conditions, the probability of relatively strong k * increments of ±0.5 is approximately twice as high compared to increment statistics computed without conditioning by sky type. Additionally, spatial autocorrelation structures of k * increment fields differ considerably between sky types. While the profiles for overcast and clear skies mostly resemble the predictions of a simple model published by Hoff and Perez (2012), this is not the case for mixed conditions. As a proxy for the smoothing effects of distributed PV, we finally show that spatial averaging mitigates variability in k * less effectively than variability in k * increments, for a spatial sensor density of 2 km −2 .

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“…85-50.95 • N and 6.36-6.50 • E (∼ 10 km × 12 km area) around Jülich, Germany, from 2 April to 24 July 2013. Each of these stations continuously recorded the global radiation (G in W m −2 ) using a silicon photodiode pyranometer (model: EKO ML-020VM) (King, 1997;Madhavan et al, 2016). Changes in the spectral distribution of downward irradiance compared to the conditions during calibration can lead to errors of up to 5 %, particulary at higher solar zenith angles.…”

Section: Data Setsmentioning

confidence: 99%

Multiresolution analysis of the spatiotemporal variability in global radiation observed by a dense network of 99 pyranometers

et al. 2017

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Abstract. The time series of global radiation observed by a dense network of 99 autonomous pyranometers during the HOPE campaign around Jülich, Germany, are investigated with a multiresolution analysis based on the maximum overlap discrete wavelet transform and the Haar wavelet. For different sky conditions, typical wavelet power spectra are calculated to quantify the timescale dependence of variability in global transmittance. Distinctly higher variability is observed at all frequencies in the power spectra of global transmittance under broken-cloud conditions compared to clear, cirrus, or overcast skies. The spatial autocorrelation function including its frequency dependence is determined to quantify the degree of similarity of two time series measurements as a function of their spatial separation. Distances ranging from 100 m to 10 km are considered, and a rapid decrease of the autocorrelation function is found with increasing frequency and distance. For frequencies above 1/3 min −1 and points separated by more than 1 km, variations in transmittance become completely uncorrelated. A method is introduced to estimate the deviation between a point measurement and a spatially averaged value for a surrounding domain, which takes into account domain size and averaging period, and is used to explore the representativeness of a single pyranometer observation for its surrounding region. Two distinct mechanisms are identified, which limit the representativeness; on the one hand, spatial averaging reduces variability and thus modifies the shape of the power spectrum. On the other hand, the correlation of variations of the spatially averaged field and a point measurement decreases rapidly with increasing temporal frequency. For a grid box of 10 km × 10 km and averaging periods of 1.5-3 h, the deviation of global transmittance between a point measurement and an area-averaged value depends on the prevailing sky conditions: 2.8 (clear), 1.8 (cirrus), 1.5 (overcast), and 4.2 % (broken clouds). The solar global radiation observed at a single station is found to deviate from the spatial average by as much as 14-23 (clear), 8-26 (cirrus), 4-23 (overcast), and 31-79 W m −2 (broken clouds) from domain averages ranging from 1 km × 1 km to 10 km × 10 km in area.

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Shortwave surface radiation network for observing small-scale cloud inhomogeneity fields

Cited by 34 publications

References 27 publications

The HD(CP)<sup>2</sup> Observational Prototype Experiment (HOPE) – an overview

The HD(CP)<sup>2</sup> Observational Prototype Experiment (HOPE) – an overview

Local short-term variability in solar irradiance

Multiresolution analysis of the spatiotemporal variability in global radiation observed by a dense network of 99 pyranometers

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Shortwave surface radiation network for observing small-scale cloud inhomogeneity fields

Cited by 34 publications

References 27 publications

The HD(CP)&lt;sup&gt;2&lt;/sup&gt; Observational Prototype Experiment (HOPE) – an overview

The HD(CP)&lt;sup&gt;2&lt;/sup&gt; Observational Prototype Experiment (HOPE) – an overview

Local short-term variability in solar irradiance

Multiresolution analysis of the spatiotemporal variability in global radiation observed by a dense network of 99 pyranometers

Contact Info

Product

Resources

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The HD(CP)<sup>2</sup> Observational Prototype Experiment (HOPE) – an overview

The HD(CP)<sup>2</sup> Observational Prototype Experiment (HOPE) – an overview