Helliconia WinterDuring winter, Helliconia is dominated by radiation from Batalix while Freyr is distant and adds little warmth to the planet. This leads to a symmetric atmospheric circulation pattern as most energy reaches the equator. As we've seen in the previous section, glaciation sets in during autumn and has covered most of the planet short of the tropical regions at Freyr apoapsis. The chief region that the tropics are not ice-covered is however not temperature - that is very low even there, it is that most of the moisture in the atmosphere has been frozen out by the time the tropics cool.The simulation file is availabe as example24.cfg. A few parameters are changed with respect to the summer scenario: First, snow albedo is assumed to be lower. As the atmosphere is very frigid, there is little fresh snowfall occurring, and so the surface of the snow can age and show dirt. Second, CO2 content of the atmosphere is assumed to be higher since there is little active biosphere to remove CO2, so whatever is produced by volcano eruptions can accumulate in the atmosphere. Third, due to the low temperature water vapour in the atmosphere is much reduced as compared with summer. And finally, cloud development is assumed to be somewhat reduced.
Winter climateThe resulting winter is very harsh - temperatures rarely exceed 250 K and can drop as low as 190 K (-83 deg C) when Batalix is not visible in the sky.
This begs the question whether the planet can actually support a limited biosphere as Aldiss describes - clearly large herds of yelk need something to feed on, but it is difficult to imagine plant growth at such harsh conditions. Can Helliconia winters be warmer? Even a larger CO2 content does not achieve this because water as the main actor remains frozen out - also albedo of snow cannot be very low (and Aldiss describes plenty of snow), so it seems difficult to come up with any scenario that traps more of the incoming radiation - I at least have not managed, and this prompts the question - to what degree did Aldiss actually know the physics of the planet? Possible errors in the novelsThe first Helliconia novel was published in 1982, and at that time a computation like the worldbuilder does would have required a supercomputer (if it was possible at all), so Aldiss could simply not have done it and likely was limited to analytic estimates. Nevertheless, a few things seem out of place, and a few more seem odd given the more detailed simulation results.
MyrkwyrThe day of Myrkwyr supposedly marks the time when Freyr disappears from the northern polar region for most of the winter as observed at Kharnabhar - which lies roughly on the arctic circle. These two facts exclude each other - on the arctic circle by definition the Sun is absent for a day only - only at higher latitudes that absence becomes an extended period of time.Of course it could be that Freyr is not in the same orbital plane as Batalix, then Kharnabhar might lie way beyond the Freyr arctic circle. The problem with this is that it makes the icecap problem to be discussed in the following only worse. It could also be that Freyr only drops below the local horizon (a mountan range) - but then Myrkwyr wouldn't mark any day in particular, it would just apply to one specific location.
The northern icecapAs we've seen in the previous chapter, during summer the temperatures in the northern polar region are very hot despite the high albedo of ice - frequently above 40 deg C (and that is the whole day - Freyr does not set). Condisions like that last for more than a hundred years even while this is a small portion of the orbit around Freyr. Based on lake-ice melting in spring, this would imply that at least a 10 m thick layer of ice can melt per year, implying a loss of more than 1000 m of ice per summer.(Obviously the dynamics of the southern ice cap is different in that it never really gets warm and melts to a significant degree.) When and how does the northern ice cap get replaced? It must happen during autumn freezing and spring when the northern hemisphere is warm enough to already permit significant precipitation, yet cold enough to make that precipitation snow (currently the simulation does not consider local atmosphere temperature for precipitation, so this can't really be calculated yet). But even if that mechanism works, it would require 10 times as much thickness as snow as it needs to replace ice - a grand total of 10.000 m of snowfall. This is huge and for an autumn/spring phase that lasts a mere 100 years, it requires some 500 m of snowfall per year. The obvious conclusion is that the dynamics is much favouring a more asymmetric ice distribution on which the northern hemisphere never has a significant ice cap.
BiomassAldiss remarks in the appendix that biomass in winter is roughly a third from what it is in summer, following the amount of radiation. The problem with that statement is that this is incoming radiation, but what's missing is that albedo is much higher in winter due to the snowcover, and so the available energy in winter is much lower than a third.Generally the issue is that biochemistry is hard-pressed to work at such low temperatures - for instance standard photosynthesis is absent in terrestrial winters, and even if it were not, high piles of snow would cover most plantlife. Thus it is somewhat unclear what exactly the input of the food chain in Helliconia's winter ecosystem is supposed to be.
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