This time the question answered relates to the extraterrestrial and ground-level solar spectra. One of ours readers noticed an error in a figure in a book, and asked how to draw a similar figure but avoiding this problem. We provide R code showing how to plot the figures and where to find the spectral data.Non peer reviewe

Aphalo, Pedro J.

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Helsingin yliopiston digitaalinen arkisto

UV4Plants Bulletin, 2020, no. 1 Questions and AnswersPedro J. Aphalo, ORCID: 0000-0003-3385-972XViPS, Organismal and Evolutionary Biology, University of Helsinki, Helsinki,FinlandDOI: 10.19232/uv4pb.2020.1.25 © 2020 The Author, licensed underI had planned to start this section in the next issue and inviting readers tosubmit questions in this one. However, when we were about to go to press Ireceived one interesting question, so here we launch the new section!Please, submit your questions to mailto:reader.questions@uv4plants.org. I will answer those I am can, and forward other experts otherwise. Notall questions and their answers will be published, but we will attempt toquickly answer all of them through e-mail.Extraterrestrial and ground-level solar spectrumQ1: I was reading some literature with respect to the atmosphere and some-thing keeps me puzzled. In the ASPB book “The molecular life of plants”(Jones, 2013; Page 280) they show a figure of the solar spectrum.The red graph starts at 280 nm (extraterrestrial) while the blue one (groundlevel) starts at 300 nm. The thing I am wondering, how is it possible that atthe top of the atmosphere there are no shorter wavelengths than 280 nm? Forall I know at least UV-C (200 nm) should reach the ozone layer (Stratosphere).It makes me wonder if they only measured from 280nm onwards. What areyour thoughts about this?A1: Well spotted! You are correct, the extra-terrestrial solar spectrum istruncated in the figure. When these spectra are used in models as input forcomputing the spectrum at ground level, the shorter wavelengths are of nointerest, but for the figure, of course, they are highly relevant!I plotted the spectrum that the World Meteorological Organization nor-mally uses. It comes from: Wehrli, C. (1985) Extraterrestrial solar spectrum.Pub. No. 615, World Radiation Center, Davos, Switzerland. The ASTM spec-trum for global radiation is for 1.5 air-masses so for roughly an average year-round sun elevation for mid-latitudes. If you need data to make a fresh plotwith both spectra, equivalent to the one you sent, the necessary data are all inmy R package ‘photobiologySun’. If you use R (even if just a little) and want7312 P. J. Aphalo: Questions and Answersannotated versions I can show you how to rather easily plot the combinedplot.library(photobiologySun)library(ggspectra)autoplot(sun_reference.mspct[c("WMO.Wehrli.AM0", "ASTM.G173.global")],annotations = "", range = c(50, 3000))0.00.51.01.52.01000 2000 3000Wavelength (nm)Spectral  energy  irradiance  E(λ)  (W m−2 nm−1)spct.idxWMO.Wehrli.AM0ASTM.G173.globalA1’: Thank you for the fast reply and the help with getting the full data! Iam very unfamiliar with R but I managed to get the graph from the code yousent over.Q2: I am now trying to format the graph in R in a similar fashion as the orig-inal Graph I originally sent you but this also seems to fail. Any suggestionson this?A2: Here are two examples that get you quite close to the original plot. Ihope the code is not too intimidating…If you do not mind, I will include yourquestion and this answer as a “Reader’s question” in the UV4Plants Bulletin.It could be useful to others in addition to you and me. ;-)ggplot(clip_wl(sun_reference.mspct[c("WMO.Wehrli.AM0", "ASTM.G173.global")],range = c(NA, 3000))) +aes(color = spct.idx) +geom_line() +scale_color_manual(name = "", labels = c("AM0", "AM1.5"), #values = c("purple", "blue")) +scale_x_wl_continuous() +74UV4Plants Bulletin, 2020, no. 1scale_y_s.e.irrad_continuous(expand = c(0, 0)) +annotate(geom = "text",x = c(750, 950, 1150, 1450, 1900),y = c(0.1, 0.1, 0.7, 0.5, 0.3),label = c("O[2]", "H[2]*O", "H[2]*O", "H[2]*O", "H[2]*O~CO[2]"),parse = TRUE) +theme_classic() +theme(legend.position = "top")O2 H2OH2OH2OH2O CO20.00.51.01.52.0500 1000 1500 2000 2500 3000Wavelength, λ (nm)Spectral energy irradiance, Eλ (W m−2 nm−1)AM0 AM1.5ggplot(clip_wl(sun_reference.mspct[c("WMO.Wehrli.AM0", "ASTM.G173.global")],range = c(NA, 3000))) +aes(linetype = spct.idx) +wl_guide(alpha = 0.15, color = NA) +geom_line() +scale_linetype_discrete(name = "", labels = c("AM0", "AM1.5")) +scale_x_wl_continuous(expand = c(0, 0),breaks = c(200, 300, 400, 700, 1000, 1500, 2000, 2500)) +scale_y_s.e.irrad_continuous(expand = c(0, 0)) +annotate(geom = "text",x = c(750, 950, 1150, 1450, 1900),y = c(0.1, 0.1, 0.7, 0.5, 0.3),label = c("O[2]", "H[2]*O", "H[2]*O", "H[2]*O", "H[2]*O~CO[2]"),parse = TRUE) +theme_classic() +theme(legend.position = "top")7512 P. J. Aphalo: Questions and AnswersO2 H2OH2OH2OH2O CO20.00.51.01.52.0200 300 400 700 1000 1500 2000 2500Wavelength, λ (nm)Spectral energy irradiance, Eλ (W m−2 nm−1)AM0 AM1.5A2’: Thank you very much. Hope to see you on the next UV4PLANTS meet-ing!Regular column, not peer reviewed.Published on-line on 2020-09-12.76

Extraterrestrial and ground-level solar spectra

https://helda.helsinki.fi/bitstream/10138/326213/1/88_Article.pdf

Extraterrestrial and ground-level solar spectra

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