Helliconia SummerWe start with a simulation of Helliconia at periapsis since we know the temperature of the planet at this point as 283 K. As discussed previously, we can infer that the northern hemisphere is tilted towards Freyr at this point (for instance from the fact that Myrkwyr hides Freyr from the northern hemisphere as winter sets in), although the novels do not specify at what point in orbit this tilt is maximal, and neither do they specify whether there is a tilt in the orbital planes of Batalix and Freyr, so for simplicity we assume such orbital plane tilt is absent.This means that during summer Freyr never sets in the northern hemisphere, which as a result becomes the hottest spot on the planet, with the south pole being the coldest spot. Such irradiation forces an asymmetric circulation pattern in which the equator is not the main convection zone (and we may assume that it also massively reduces the northern ice shield). Such a pattern is forced by requiring circulation_pattern 10 in the weather section. The layout of Helliconia's surface has been read off from Aldiss' map provided in the appendix of the novels, and parameters for the albedo and thermal inertia are chosen Earth-like. The atmosphere has been investigated in the previous section already. The complete set of files used for this simulation is found as example23.cfg, material_map_helliconia.cfg and materials_helliconia.cfg Thermal propertiesGenerally temperatures are high on the northern hemisphere both in conjunction and opposition of Freyr and Batalix, but the equatorial zone is quite viable. Compared with the atmosphereless temperatures discussed earlier, one can easily see that a lot of transport is happening:
While the northern polar region must see plenty of ice melting, the southern polar region never actually thaws even when fully illuminated by Batalix. Looking at the surface-averaged temperature over time reveals an oscillation with the amplitude of the orbital period around Batalix. By disabling the forest fire contribution we can also have a look at the role of this feedback mechanism to stabilize the temperatures during the hottest part of the cycle (i.e. th conjunction).
Clouds and weatherCloud patterns on Helliconia are driven by the circulation model which leads to strong convective development around the northern polar region and a ridge suppressing convection at around 60 degrees latitude as clearly seen in the following cloud diagram:
Climate diagrams can be extracted for various surface locations, as an example is here Pannoval in the equatorial region on Campannlat:
The daily temperatures are high (and vary from about 28 to 36 degrees) and the location shows a seasonal variation of precipitation with a dry and a wet period. Especially in conjunction, temperatures close to the northern arctic circles are very hot (and dry, as the ridge blocks convective cloud formation) as the chart of Kharnabhar demonstrates:
The southern continent of Hespagorat is much cooler - here is the chart for Lordryardry on the coast:
The mean temperature is below zero year-round with frequent precipitation.
Autumn cooling and glaciationFollowing the cooling of the planet as it moves along its orbit around Freyr is not straightforward, as a couple of things can be expected to change. First of all, at some point Helliconia's irradiation is no longer pole-dominated and the equator becomes the hottest region. This happens between 60 and 70 orbital periods (86 to 101 years), and consequently at some point the simulation needs to be switched to a standard circulation pattern.Second, the water vapour content of the atmosphere would almost certainly change somewhat, along with possibly cloud formation. Methane outgassing might cease along with biosphere activity that removes CO2 from the atmosphere, so the composition of the atmosphere is not a given. Keeping this in mind, just simulating ahead with the summer parameters and changing circulation pattern at 70 orbital periods reveals the following temperature drop:
This clearly reminds of the Ice Age pattern - an initially small temperature change reaches a tipping point and over a period the temperature drops much more rapidly as glaciation sets in and albedo increases.
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