solar radiation term in heat budget

[mrke]

plantecophys/R/LeafEnergyBalance.R

Line 161 in c974982

Rsol <- 2*PPFD/UMOLPERJ # W m-2

Hi Remko,
I was comparing the predictions of leaf temperature from FindTleaf with other approaches and found that FindTleaf predicted way too high. I think it is because you multiply the incoming solar by two at the line referenced above. I think instead, because only one side gets the full blast, and the other side should get what is reflected from whatever surface is below.
All the best,
Mike

[mrke]

sorry I missed a bit - should have said 'I think instead, you should either just multiply by 1 or be explicit about reflected solar hitting the underside ...'

[RemkoDuursma]

Hi Mike, thanks for the info. We never really tested the Tleaf predictionsnin detail, so i am not surprised there is some error. Thanks for letting me know. Are you able to make a pull request with the suggested change? Otherwise i can fix it soon. I have left science so it may take a little longer unfortunately. greetings Remko

…

On Mon, 11 Dec 2023, 21:20 Michael Kearney, ***@***.***> wrote: https://github.com/RemkoDuursma/plantecophys/blob/c9749828041f10ca47c6691436678e0a5632cfb8/R/LeafEnergyBalance.R#L161 Hi Remko, I was comparing the predictions of leaf temperature from FindTleaf with other approaches and found that FindTleaf predicted way too high. I think it is because you multiply the incoming solar by two at the line referenced above. I think instead, because only one side gets the full blast, and the other side should get what is reflected from whatever surface is below. All the best, Mike — Reply to this email directly, view it on GitHub <#5>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AADOOCW2VT3DJI2BMNDO6HTYI5THHAVCNFSM6AAAAABAQLDCH6VHI2DSMVQWIX3LMV43ASLTON2WKOZSGAZTMNBWGA2DSNI> . You are receiving this because you are subscribed to this thread.Message ID: ***@***.***>

[RemkoDuursma]

right thanks

…

On Mon, 11 Dec 2023, 21:22 Michael Kearney, ***@***.***> wrote: sorry I missed a bit - should have said 'I think instead, you should either just multiply by 1 or be explicit about reflected solar hitting the underside ...' — Reply to this email directly, view it on GitHub <#5 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AADOOCRVQBTIWMBHIPCDZELYI5TRDAVCNFSM6AAAAABAQLDCH6VHI2DSMVQWIX3LMV43OSLTON2WKQ3PNVWWK3TUHMYTQNJQHAZDQOJWGY> . You are receiving this because you are subscribed to this thread.Message ID: ***@***.***>

[mrke]

Actually, I take it back - I think the x2 might be because you are assuming 0.5 of the global solar is PAR and so multiplying the PPFD by two

[s-kganz]

Hi,

I'm also finding that FindTLeaf returns too high of temperatures. The supplemental of this paper reports the same thing, especially when leaf size is large. I think the issue is coming from the treatment of longwave radiation:

plantecophys/R/LeafEnergyBalance.R

Lines 156 to 167 in c974982

	# Longwave radiation
	# (positive flux is heat loss from leaf)
	Rlongup <- Emissivity*Boltz*Tk(Tleaf)^4
	# Rnet
	Rsol <- 2*PPFD/UMOLPERJ # W m-2
	Rnet <- LeafAbs*Rsol - Rlongup # full
	# Isothermal net radiation (Leuning et al. 1995, Appendix)
	ea <- esat(Tair) - 1000*VPD
	ema <- 0.642*(ea/Tk(Tair))^(1/7)
	Rnetiso <- LeafAbs*Rsol - (1 - ema)*Boltz*Tk(Tair)^4 # isothermal net radiation

My understanding about longwave radiation is that:

1. Both sides of the leaf are radiating energy
2. Longwave radiation is emitted by air in all directions, so both sides of the leaf receive the incoming flux

This would translate to multiplying both Rlongup and (1 - ema)*Boltz*Tk(Tair)^4 by 2 in the above snippet. I've been working on some energy balance models that are formulated similarly, and I find that this results in more reasonable (i.e. cooler) temperatures. I don't have permission to share data from that project, but if this is of interest I could find something in the literature to compare on.