Today marks the high point of summer, exactly halfway between Jun 21 and Sep 21, for us northerners. Have you ever noticed that the hottest time of year does not correspond to the day of longest sunshine? Theoretically, the maximum amount of sunlight comes to us in the twelve weeks surrounding the summer solstice: six weeks prior, May 7, six weeks after, Aug 7. But the summer season is from the longest day to the autumnal equinox. Why isn’t summer from May 7 to Aug 7? Also, have you ever noticed that we celebrate the first day of a season rather than the peak of a season? Isn’t that strange? You would think that the height of a season is when that season is best represented with a holiday, rather than the first day.

Well it turns out that the ocean plays a huge factor in the heating and cooling of the planet, and water has a much higher specific heat capacity than air. Specific heat capacity is essentially the amount of heat it takes to raise something’s temperature by 1 degree. As anyone who has tried to boil water knows, it takes way longer to heat water than it does to heat the air. An open flame will heat air easily, but it takes some time to heat a pot of water. Likewise, water can keep warm for a while, as anyone who has let a pot of coffee sit out or tried to sip soup ten minutes after boiling. Water takes a lot of energy to heat, and because it stores more energy per temperature degree, cooling takes longer as well. Water requires more energy input for heating and releases more energy in cooling than air, which is why the seasons are offset from the solar calendar.

It turns out that, in California at least, the ocean is coldest in February/March, and is warmest in September. So if we approximate the peak of oceanic summer (the ocean’s hottest time of year) as mapping onto the fall equinox, and the peak of oceanic winter (the ocean’s coldest time of year) as mapping onto the spring equinox, then we get two seasonal systems that work in conjunction. The solar seasonal system and the oceanic seasonal system. The oceanic seasonal system is delayed because of water’s higher specific heat capacity. (There could also be an atmospheric seasonal system accounting for the specific heat capacity of the air, but let’s ignore that for now, since air heats up and cools down relatively quickly, e.g., within 24 hours air temperature can swing wildly.)

Solar seasons:
Winter: Nov 7-Feb 7, solstice Dec 21
Spring: Feb 7-May 7, equinox Mar 21
Summer: May 7-Aug 7, solstice Jun 21
Fall: Aug 7- Nov 7, equinox Sep 21
Oceanic seasons:
Winter: Feb 7-May 7, mininum Mar 21
Spring: May 7-Aug 7, isotherm Jun 21
Summer: Aug 7-Nov 7, maximum Sep 21
Fall: Nov 7-Feb 7, isotherm Dec 21

Ask any surfer or sailor, and they can tell you all about the ocean’s changes through the year. So why are our seasons set differently than these? Our standard seasons are right in the middle of these.

Standard seasons:
Winter: Dec 21-Mar 21, minimum Feb 7
Spring: Mar 21-Jun 21, median May 7
Summer: Jun 21-Sep 21, maximum Aug 7
Fall: Sep 21-Dec 21, median Oct 7

The standard seasons represent the combined system of sunlight and ocean temperature cycles. Those of us closer to the coast know how the warm months extend well into October. I remember leaves in San Diego not falling until January some years. This is because of the ocean’s high specific heat capacity. Oceanic summer overlaps with solar autumn, so you get faint light with warm air, an Indian Summer. This is also why high places can be snow-free until November yet have snow flurries into June. The net amount of thermal energy on the planet is a combination of solar radiation and the slow-reacting sponge-like nature of the ocean. In coastal California, this explains why spring is hazy and breezy—cold ocean, warming air pushes the cold ocean and stirs the ocean—why summer is foggy—warming but still cool ocean, lots of sunlight, steams up into cold fog banks—why fall is clear and balmy—warm ocean, gentle light, few clouds, nice weather—why winter is rainy and crisp—cooling ocean, low light, water relaxes down from the sky.

Solar seasons:
Winter: Nov 7-Feb 7, solstice Dec 21
Spring: Feb 7-May 7, equinox Mar 21
Summer: May 7-Aug 7, solstice Jun 21
Fall: Aug 7- Nov 7, equinox Sep 21
Standard seasons:
Winter: Dec 21-Mar 21, net energy minimum Feb 7
Spring: Mar 21-Jun 21, median May 7
Summer: Jun 21-Sep 21, net energy maximum Aug 7
Fall: Sep 21-Dec 21, median Oct 7
Oceanic seasons:
Winter: Feb 7-May 7, mininum Mar 21
Spring: May 7-Aug 7, isotherm Jun 21
Summer: Aug 7-Nov 7, maximum Sep 21
Fall: Nov 7-Feb 7, isotherm Dec 21

This isn’t perfectly tuned, but it gets the point across. We could get into the nitty gritty about latitude, specific heat capacities, elevations, etc. But for central coastal California, this works pretty well. It’s a supremely average place. From Aug 7 onward, the net temperatures (of the northern hemisphere) slide downhill, until about Feb 7, when the combination of low sunlight and cooling ocean reach a trough. Summer hereon declines, mosquitos in the mountains abate, marmots cease from their radiator fluid gobblings, acorns cascade.

At the heart of the land of the golden mean is a steep gradient, reflecting the intersectional, asymptotic nature of natural bisections.


Happy Net Energy Maximum Day
from Gorda