Sa Ji Tario wrote: ↑
Thu Jul 08, 2021 1:21 pm
isoparix wrote: ↑
Thu Jul 08, 2021 11:12 am
'Of course, the distance from the Sun doesn't determine the seasons.'
Of course not.
But 3% further away is 3% more distant and therefore surely , means (1/1.03)^2, or approx 6%, less insolation? And a difference of 6% between min and max energy received ought to have some traceable impact on the weather?
Isoparix, Although it is closer to the sun in the summer of the southern hemisphere, the difference in energy received is moderated with the larger illuminated water surface
>>>>Wikipedia https://en.wikipedia.org/wiki/Apsis#Per ... d_aphelion
Because of the increased distance at aphelion, only 93.55% of the radiation from the Sun falls on a given area of Earth's surface as does at perihelion, but this does not account for the seasons, which result instead from the tilt of Earth's axis of 23.4° away from perpendicular to the plane of Earth's orbit. Indeed, at both perihelion and aphelion it is summer in one hemisphere while it is winter in the other one. Winter falls on the hemisphere where sunlight strikes least directly, and summer falls where sunlight strikes most directly, regardless of the Earth's distance from the Sun.
In the northern hemisphere, summer occurs at the same time as aphelion, when solar radiation is lowest. Despite this, summers in the northern hemisphere are on average 2.3 °C (4 °F) warmer than in the southern hemisphere, because the northern hemisphere contains larger land masses, which are easier to heat than the seas.
The above Wikipedia article references the following, which has a bit more detail.
[The following includes quotes of: Roy Spencer of NASA's Global Hydrology and Climate Center (GHCC).]
But there's more to the story: Says Spencer, "the average temperature of the whole earth at aphelion is about 4°F or 2.3°C higher than it is at perihelion." Our planet is actually warmer when we're farther from the Sun!
Above: Earth's land-masses are concentrated more north of the equator than south. Image credit and copyright: the PALEOMAP Project.
This happens because continents and oceans aren't distributed evenly around the globe. There's more land in the northern hemisphere and more water in the south. During the month of July the land-crowded northern half of our planet is tilted toward the Sun. "Earth's temperature is slightly higher in July because the Sun is shining down on all that land, which heats up rather easily," says Spencer.
Physicists would say that continents have low heat capacity. "Consider the desert," says Bill Patzert, an oceanographer at NASA's Jet Propulsion Laboratory. "At night the desert is cold, perhaps only 60° F (16° C). When the Sun rises in the morning the temperature might jump to 100° F (38° C) or more." Such mercurial behavior is characteristic of materials like rocks and soil with low heat capacity. It doesn't take much sunlight to substantially elevate their temperature.
Water is different. It has high heat capacity. "Let's say you went sailing off Malibu Beach at noon," continues Patzert. "The offshore temperature might be 75° F (24° C) -- pretty pleasant!" What happens after sunset? "The temperature drops, but only a few degrees because the heat capacity of the ocean is so high."
All this explains why July is our planet's warmest month: Northern continents baked by the aphelion Sun elevate the average temperature of the entire globe. January, on the other hand, is the coolest month because that's when our planet presents its water-dominated hemisphere to the Sun. "We're closer to the Sun in January," says Spencer, "but the extra sunlight gets spread throughout the oceans." Southern summer in January (perihelion) is therefore cooler than northern summer in July (aphelion).
I'm not sure I fully understand the data, statements, and reasoning in this last part. What it seems to be saying is:
If you measure temperature of the air about 2 meters off of the surface, and if you sample that all around the globe on a given date and average the numbers, then you'll find a higher average in July than in January. This is in spite of the fact that the "heat budget" in July begins with less solar radiation hitting the planet than in January. And they're saying that the radiation is heating more water in July, raising it only x degrees, say, on average, whereas in January, more radiation hits terra firma and the temperature above such land jumps a bunch more than x degrees.
A detailed view would perhaps be done by dividing the Earth's surface into a massive number of small cells and observing the heat exchange going on in each unit over time. And then you'd want to include heat exchange from one cell to its neighbors as well, and weather and ocean currents might need to come into play -- but maybe you could do a good representation of the overall effect we're discussing, without all of that.
I assume someone (very likely Dr. Spencer) has already done this, since it sounds like just the very beginning of any decent weather model.
But what I find interesting here is that in January, the Earth is in some sense almost certainly "warmer" than it is in July, but the average air temperature felt by surface dwellers is lower in January, and that's not just because most of us live in the northern hemisphere, it's actually a true average over all points that are 2 meters off of the surface of the globe.
At least that's how I'm reading this.