Stump the Meteorologist

'temperate boundary called the Horse latitudes'



is that grey Horse latitudes?

please say it isnt.

Don't tempt him. He's as bad as I am if you get him started on the right topics.

I should have a discussion of climate effects around the world up later today.

Horse latitudes is actually quite grim.

As the story goes, when Spain and Portugal were conquering, consolidating and colonizing their New World holdings, they sent tens of thousands of unfortunate horses across the Pacific.

When the ships would sometimes become becalmed in the middle of the ocean for weeks at a time, often running out of water, the poor beasts were allowed to die of thirst so the people could live.

Their bloated carcasses were dumped unceremoniously over the side where they would get caught up in the great North Atlantic Gyre and South Atlantic Gyre, along with all the other debris from ships and shipwrecks, where they apparently floated for an amazingly long time.

(These gyres have now become choked with all the plastic from 4 continents for the last half century. The total area of plastic is the size of a continent itself. But that would be a topic for Big Bad Serious.)

halfwise wrote:Okay Dave, it seems like from all I can fathom the only reason for strong winds around the tip of Cape Horn is the complete absence of land at that latitude. Holds both for the westerlies and the easterlies further south. Easy enough?

If everything were that easy, think of all the meteorologists who would be out of jobs!
Are you sure you can't muddy the waters a little in the interest of job security?

its pretty horrific that plastic continent floating in the sea, I wish someone would do something about it.

there has been work done on plastic eating microbes. Don't know much about it, I would fear the consequences if it got loose.

But yes Dave, I think it really is that simple. I was trying to come up with something more complicated using the boundary between warm and cold air masses, but the direction would come out wrong. At least the kids will understand the low friction explanation. Also tell them we'd often have stronger winds all over if not for the friction: they blow pretty good aloft.

Geography and Climate

One might naturally suppose that two places at the same latitude in different parts of the world would get the same amount of sunlight, and so would have the same seasonal temperature patterns. This would be true if temperature were completely controlled by the sun, but not only do clouds get in the way of the sun, but winds blowing from different directions or over different surface features can bring their own contributions to the temperature bath. And of course the oceans bring their warm or cold currents to bear as well. So let’s go back and take a look at global circulation.




In this diagram the prevailing winds are shown in purple dashed lines, the ocean surface currents (driven by the winds) are shown in black. We already know about things like the Gulf stream bringing warm water up the US east coast to finally warm and cause fog in Britain, (while the US west coast has cold currents), but now we want to discuss the winds.

Before we discuss the prevailing surface winds we must think about the locations of ascent and descent. At the equator the air is ascending, and with all that warm moist air rising the result is a band of clouds. Clouds also precipitate, removing moisture from the air, drying it out (have you ever noted that the air is often muggy before a rainstorm, but dry and refreshing after?). But this dried out air descends around 30 degrees latitude. And guess what? Here we find the deserts: the Sahara, Mohabi and Gobi in the north; the Nazga plains and the Australian outback in the South. The 60 degree line is where air is ascending again, so we get the temperate rainforests of Canada and Siberia (actually distorted by the continents to lower than 60 degrees, but round numbers are nice).

Now we turn our attention to the surface winds. Clearly in the temperate zones the west coasts will have prevailing winds coming over the oceans while the east coasts have prevailing winds coming over the land. This holds for both Northern and Southern hemispheres. Other than bringing more humidity, what else will these winds bring? Since most cities are on coasts this is a rather interesting question.

It turns out if you shine sun on water and on soil/rock, the water will not heat up as fast. There are several reasons for this: evaporative cooling is one, intrinsic differences in heat capacity is another; but the most important reason that water is harder to heat up than land is that it mixes around. During the course of a day the sun would warm up the top few centimeters of soil; but water will stir around and the same heating power ends up being applied to a full meter of water, more or less. And the same goes for cooling: soil will cool off quickly, while the top layer of water will cool and sink only to present you with the next layer, so it takes longer to cool down.

So the oceans have a moderating effect on temperature, not swinging as widely as the land during the day/night cycles or the summer/winter cycles. One immediate effect of this is the seabreeze: during daytime the coast will heat up more than the water, air will rise over the land and suck in more air behind it. At night the ocean is warmer and this reverses. Anyone who lives near the beach can attest to this.

But this ocean moderating influence then becomes applied to western coasts due to the prevailing wind. In the US California never becomes as hot in summer nor as cold in winter as the East coast. Since all of Europe is the more or less the west coast of Eurasia, it will experience milder temperature swings than cities at the same latitude in China, or on the US East coast for that matter. This and the remnants of the Gulf Stream keep the British isles from having as brutal winters as their counterparts in Canadian Labrador.

But there’s another moderating effect going on, and to understand it we have to delve into the inner workings of High and Low pressure systems. There’s actually three different ways for pressure systems to be formed, but fortunately our goal requires us to look into the easiest to understand.

When air is heated, it expands. Everyone’s immediate reaction is to shout out ‘it rises!’, and that’s right, but leave that alone for a while and look at what happens when a whole column of air expands.




So the warm column has expanded so that it’s taller than the cooler columns of air around it (left). Since there’s the same mass of air in each column the pressures at the surface will initially be the same, but that won’t last because the air in the taller column will spill over onto the cooler shorter columns. Now we have the situation on the right, where the cooler columns have more mass in them, so there is higher pressure at the bottom, and lower pressure at the bottom of the warm column. Naturally at the bottom the air will now flow from high to low, while at the top it will flow from the high stack to the low stack, and we get this continuous circulation.

Local areas of higher temperature will form low pressure systems (and cool temperatures will form high pressures).

One more twist and we’re almost there. In the diagram above we show air flowing straight towards the low pressure. But when we’re talking about pressure systems that are hundreds of km across, this can take the better part of a day, and the coriolis effect comes into play. We’re gonna concentrate on the Northern hemisphere and the Aussies will just have to stew. If we look at the pressure systems from above, the surface winds heading into a low pressure or out of high pressure system will curve to the right:




If the air finds the right circular groove the pressure and coriolis forces will cancel each other just right to allow the air to continue in a perfect circle. There is a tendency for air to find this nice little groove, so once the dust settles the wind tends to blow counter clockwise (CCW) around a low, CW around a high.

What’s this got to do with climate? Well, in the summer the land is generally warmer than the ocean, so there’s a big low pressure system over it. Superimposed on the general easterly or westerly flow is a big rotation. This tends to add or subtract to the east and west flows, but adds in a north or south component that wasn’t there before. Let’s look at North America in the summer and winter:





We see that in the summer the predominant Low brings warm air up from the south on the east coast in summer and cold air down from the north in winter, accentuating the seasonal contrast. But on the west coast, cool air comes down from the north in the summer, and warm air comes up from the south in winter, moderating the seasonal constrasts. That’s why in America people like to live in California, but the west coast is know for it’s extremes in climate.

Most of Europe might be considered the west coast of Eurasia, bringing it milder seasonal contrasts than what might be experienced in China.

Which brings us to Naples versus New York. By the previous argument we’d expect Naples to have milder winters and summers than New York, especially since the prevailing winds from the west would blow across the mediterranean. Indeed the winters are a good 5 or 6 degrees centrigrade warmer on average than New York. But the summers are about the same temperature, why?

I expect the reason for this is that in summer the continental low would send wind down from the north, coming across the Alps. The mountains lift the air, causing adiabatic cooling and condensation, which warms the air (evaporation cools it, condensation is the opposite). Moreover this dry air may have less cloud cover, leading to more solar heating. My guess is Naples has alternating cool but humid summer days when the wind is from the west, with warm but dry days when the wind is from the North. Is that right?

All that implies the world is round! ... .... ... Oh Halfy! You and your wild fancies.

I do get carried away at times.

What would you say to those who say that Climate change is just a natural phenomenon of warming/ cooling?

Also: is the jet stream now permanently warped?

Halfy is the Mediterranean sea a factor too?, it could bring warmer air in Winter? also the Alps do protect Italy from weather coming from the North I think. But having said that we get winds coming from Russia and the Balkans, so Venice and Trieste are freezing cold in Winter. I have never in my life experienced cold as bad as Venice in January. Also under Naples is a bloody great live volcano which could blow at any moment, there is an area called Campi Flegrei, which is basically hydrothermal pools which I bet heat up the whole area.


(wiki says)
The Phlegraean Fields, also known as Campi Flegrei, (from Greek φλέγος, burning), is a large 13 kilometres (8.1 mi) wide caldera situated to the west of Naples, Italy. It was declared a regional park in 2003. Lying mostly underwater, the area comprises 24 craters and volcanic edifices. Hydrothermal activity can be observed at Lucrino, Agnano and the town of Pozzuoli. There are also effusive gaseous manifestations in the Solfatara crater, which is known as the mythological home of the Roman god of fire, Vulcan. The area also features bradyseismic phenomena, which are most evident at the Macellum of Pozzuoli which in the 18th century was misidentified as a Temple of Serapis, as geologists puzzled over bands of boreholes (Gastrochaenolites) left by marine Lithophaga molluscs on three standing marble columns, showing that the level of the site in relation to sea level had varied. This area is monitored by the Vesuvius Observatory.

The caldera, which now is essentially at ground level, is accessible on foot. It contains a large number of fumaroles, from which steam can be seen issuing, and over 150 pools of boiling mud at last count. Several subsidiary cones and tuff craters lie within the caldera. One of these craters is filled by Lake Avernus. In 1538, an eight-day eruption in the area deposited enough material to create a new hill, Monte Nuovo. It has risen about 2 metres (7 ft) from ground level since 1970. It is a volcano capable of producing VEI 7 eruptions, as large as that of Tambora in 1815.[8] At present, the Campi Flegrei area comprises the Naples districts of Agnano and Fuorigrotta, the area of Pozzuoli, Bacoli, Monte di Procida, Quarto, the Phlegrean Islands (Ischia, Procida and Vivara).

Rigby - given the following:

• strong correlation between CO2 and Temperature seen in ice cores in the past
• strong recent upswing in CO2 since careful measurements have been made since 1950 with careful assessments showing that most of this is due to us (look up "Keeling Curve")
• the lack of any extraterrestrial causes such as changes in sun intensity or orbit (also linked to climate changes in the past: look up "little ice age")

it's a pretty sure thing that the average global temperature change of 0.1 C per decade since 1880 is due mainly to us. There are problems with referring to global warming because there's a lot of variability from place to place and there can be feedbacks such as increased cloud cover due to increased evaporation which can cool the surface, which is why it's better to refer to "global climate change" as you did rather than "global warming" as many skeptics do.

But yes, given what we've been up to, there's no question we are having an effect, in fact it's a physical certainty. The complication is exactly what form that effect will take. Skeptics misread arguments about this as saying there's no consensus on whether humans are affecting the climate, but that's the wrong interpretation.

Figgs - yes I did refer to the Mediterranean in the second to last paragraph, and it's probably the dominant effect on the climate of Naples. Didn't think about effects from the Northeast, I would think that would be rare in winter unless the Mediterranean is big enough to induce a low, I guess it might be!

I was really talking off the top of my head, I didn't investigate the predominant patterns from the climatology, which probably was a mistake since I don't follow European weather and it's a very different shape from the US. Hard to know if something is big enough to change the regional weather patterns, and the Med. is kind of on the borderline in that respect.

Jet stream is "warped" by two things: predominant warm and cold spots on the surface, which may change due to ice cover in the arctic, and travelling waves (Rossby waves), which I assume you are not referring to. With the Arctic losing ice cover I think the polar jet would be shifted.

The jet streams really mark the boundaries between the global circulation cells discussed above: it's rare that the jet stream themselves cause changes in weather (though they can affect individual storms) but the shifting in global circulation cells definitely would.

Can they be warped with irreversible damage though?

Twist the Jet Stream too hard and shrapnel and whirling gears are likely to come flying out! Best thing to do is leave a path of thunderstorms (like breadcrumbs) in its way to lead it back to where it should be without it suspecting anything.

If greenhouse gasses are reduced enough for temperatures to drop back down will they go back to their previous state?

Dallas ?

, Chris, I do love your weird sense of humor.

hi

CC12 35 wrote:2 strange 4 me

Now that's something I never thought I'd hear Carly say!

your sarcasm hurts my friendly ways

Cool edit bro

Rigby wrote:If greenhouse gasses are reduced enough for temperatures to drop back down will they go back to their previous state?

Are you talking about reduced to normal rates of emission or reduced to normal levels?

Even if we stopped emitting all greenhouse gasses right now it would take decades for the CO2 to return to normal (pre-industrial) levels. Meanwhile we will continue to heat up because earth has not reached it's equilibrium temperature yet for our current level of CO2. Right now we'd have to go beyond CO2 control to stop the earth from warming (or reacting to the captured solar energy in other ways). I doubt there will ever be worldwide approval for stunts such as injecting extra sulfate drops into the atmosphere to reflect sunlight or the equivalent, so I'm afraid things will continue to change.

But it's not the human race that's in danger, that's pure hyperbole. It's our economy that may be in danger unless we reorient it towards climate mitigation. Lots of jobs available in jacking shoreline cities up a few feet, but I don't know if we'll be able to rework the system to make this a winning situation.