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mcrucifix / palinsol

R package to compute Incoming Solar Radiation (insolation) for paleoclimate studies. Features three solutions: BER78, BER90 and LA04. Computes daily-mean, season-averaged and annual means for all latitudes.
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True or mean solar longitude? #1

Closed ghost closed 11 years ago

ghost commented 11 years ago

Hi Michel,

Up to now, I've been using the MEAN solar longitude for the La04 insol, as suggested on his webpage: http://www.imcce.fr/Equipes/ASD/insola/earth/online/help.html#ancre1 I see you use the TRUE solar longitude in the function "Insol". Which one should I consider for paleoclimate applications?

Thanks,

Guillaume.

mcrucifix commented 11 years ago

Hi Guillaume,

It all depends what you want to do. If you want to plot a Milankovitch diagram and compare two periods (for example, 21ka with 0 ka), the recommendation is to use the true solar longitude, which describes the seasons (see reference below). Of course, if you want to integrate insolation over time, then of course you need the mean longitude.

The insol package offers both possibilities. Indeed, the function day2l converts a "calendar day" (which is defined here as the the mean longitude + 80) into a true longitude. So, if you want to know the insolation at a given mean longitude, first apply day2l to get the longitude and then Insol.

More discussion about this in :

Joussaume and Pascale Braconnot, Sensitivity of paleoclimate simulation results to season definitions, Journal of Geophysical Research: Atmospheres, 102, 1943--1956 1997