The reason there is a desert is because the Hadley and Ferrel Cells are meeting and descending along the Horse Latitudes. As that air falls from 10km up, it compresses, which causes adiabatic heating. And, at that initial altitude, it only contained 0.1g water per m3 to begin with—so, as that air reaches the ground, hot and dry, it sucks-up all the humidity, keeping the air below the threshold for making rain.
We know as a geological fact that the amount of water being sucked-up by that adiabatic heating is only a little bit more than the amount of water that the seas are evaporating. This is because, only a few thousand years ago (and in cycles repeatedly) the entire Sahara was green, due to a slight increase in evaporate and sea-breeze due to increased convection. It was only a SLIGHT increase which allowed the humidity to cross that threshold of rain-cloud formation, leading to an accumulation of moisture, plant life, driving more convection in a feedback loop that brought lakes to the Sahara. You seem to ignore the fact that the whole Sahara was green!
So, we only need to add enough additional humidity to cross the threshold of clouds, before all further evaporate becomes rain, in surplus. I’ve explained this a few times now. Are you noticing the details I point out, most of all “crossing a threshold of adiabatic desiccation”?
Erm, no, still a mistake. Let’s walk through a different format:
You have a bank account, which is auto-billed $3million a day by adiabatic downdrafts, so you are nervous about making that payment every day—especially because you are only evaporating $2million a day to add humidity to your account! You’re going $1million into debt, daily. That’s a desert.
Yet, the Sahara got 10% more sea-breeze convection, 11,000 years ago, which was enough for it to have a budget surplus—that’s like saying “Sahara’s account is being billed $3mill a day, and they were previously only able to put-in $2.9mill a day, but now Sahara is earning 10% more sea-breeze, which puts daily earnings at $3.19mill, for a surplus of $190K a day—Sahara will start forming lakes, now!” And that plant life it gets will pull more sea-breeze in a feedback, to help-out.
So, the added moisture is NOT causing “all the existing moisture to rain down.” It’s about exceeding the threshold, to generate a surplus. And we know, from Sahara’s green periods, that the desert is actually pretty close to that surplus—Sahara needed only 7% more sunlight, to drive 10% more wind!
Ok, got it now. Still, is there any way of knowing how much that is? 10% of all the water evaporating from all the seas near the Sahara is still a huge amount of water. And if we do add more water, is there any way of knowing where it will rain down, as opposed to being spread over the entirety of the Sahara and ending up basically useless?
Or is this the sort of thing where you would have to invest huge amounts into infrastructure to do this, before you can tell what affect it will have?
How quickly it rains down depends on a few factors, and we can tip those in our favor:
--> Humid Rise—humidity (just the h2o molecule) is only 18g/mol, while oxygen molecules are 32g/mol, so humid air is quite buoyant! Especially considering that water vapor reflects heat (infrared) back to the ground, creating a heat bulge beneath it. The result is that, once humidity begins to rise, it naturally pulls air in from all around it, along the ground. It begins to drive convection. Yet! That humid rise is normally billowy and easily dispersed by cross-breezes, which means that the humidity cannot rise high quickly; it mostly travels far overland, or stays in place. Your rain wanders to an unexpected location! We want to form rain clouds nearby, instead, so we need that humidity to rise really high, quickly, without being torn apart by cross-breezes. That’s where the solar concentrators help, with their tall tower at 1200C and radiant, they blast infrared into all the water vapor around them, pummeling a plume high up, carrying that vapor. Up high enough, the air pressure drops, which is key for causing a rapid cooling, and the formation of nice heavy clouds. The faster we take air from the ground up to a few kilometers, the more water it’ll still be holding. [[Only a fraction of one gram per m3 is needed for the thinnest clouds, but we could toss a few grams up and it’ll come down soon. We want the water to rain, evaporate, and rain down again, in as many cycles as it can. That gives plants time to grab it, in numerous locations, as well as time for the ground to catch some.]] When we look at water-demand for plants in the wild vs. water-resilient greenhouses, we can drop water demand ten-fold because nine-tenths of the water was lost in the leaves to evapotranspiration! As a result, if that leaf-sweat keeps rising and falling as rain as it travels further South, then the same bucket of water ends up getting ten times the use (assuming ground water is eventually used, as well).
--> Albedo—the desert rock is pretty bright, so the addition of vegetation and especially any water-bodies (!) will multiply the solar absorption, which will drive that heat-bulge and evaporation for humidity-buoyancy, to help loft water vapor and form clouds. This is how the Amazon does it—most of her clouds are her armpit fog, caused by solar-to-thermal foliage!
--> Vortices—the solar concentrators themselves can be rigged with a few flanges, to nudge their inflowing convection as it quickens toward the center, to spin that up-draft, helping it stay coherent and push higher, for rains nearby. Any Youtube video on Rocket Stoves by Robert Murray-Smith is best for enjoying such a vortex!
--> Swales—I love swales. I’ve been preaching swales since 2010. I heard, almost immediately, when Sepp Holzer started pitching his “crater gardens” … which were dug by an excavator, four feet deep. I was aghast—my favorite swales are micro-swales, a few inches deep, in flakey soils that rain seasonally, to catch it as it dribbles. That’s what they’re doing in the Sahel, south of Sahara, to stop the deserts. By halting the flow of water along the ground, keeping it for seep, roots, and another evaporation, you prolong the residence-time of each ton of water, leading to a greater equilibrium stock—that is, a high normal lake line, because each ton of water rarely ever leaves.
And, as to infrastructure before success—California could probably boost rains enough to help farmers and forests, here, without needing to conquer an entire desert the size of Europe!
Thank you for diving into the details with me, and continuing to ask probing questions!
The water brought-in by the Sahara doesn’t depend upon the area of the source; it’s the humidity times the m3 per second arriving. Humidity is low on arrival, reaching only 50% right now in Tunisia, their winter drizzles! The wind speed is roughly 2m/sec coming in from the sea, which is only 172,800m/day of drift. Yet! That sea-breeze is a wall of air a half kilometer high—that is why it can hold quite a bit.
If we need +10% of a 500m tall drift, that’s 50m; if we can use solar concentrators to accelerate convection, we can get away with less. And, we’re allowed to do an initial row that follows the shoreline closely, while a second row is a quarter kilometer inland, running parallel to the shore, where mixing of air lets you add another round of evaporate. So, we could have four rows across the northern edge of the Sahara, each row as thick as it needs to be to hit high humidity, and 10m tall, to send +10% moisture over the entire 9 million km2 of the Sahara.
How much water would we be pumping? The Sahara carries 172,800m/day flow per m2 intake surface x 500m tall x 4,000km coastline at 10g h2o per m3 = 3.5 billion tons per day, a thousand or so dead seas. (About 1.25 Trillion tons a year, enough to cover the 9 Million km2 with 139mm of rain, on average, if it had fallen instead of being sopped-up by adiabatic heat.)
We need 10% of that, or a hundred and eighty dead seas. It seems monstrous, but much of the coastline there is low for miles, so pumping 1 ton to the top of 10m at even just 20% efficiency costs 500kJ. If you want to pump that in a day, using solar, you’ll need 1/4th of a square foot of solar. That 1 ton, if we cross the threshold and it becomes surplus rain, will water 3 square meters their annual budget… and the solar is paying for that amount of irrigation every day; 1,000 m2 of rains from a dinner plate of solar, each year. It’s that energy efficiency, combined with dead simple capital expenditures, which would make something so insane potentially feasible. I’d pick California to try, first!
500kJ per ton, for 350Mil tons per day—that’s 175TJ per day, or 2 GW. That’s a nuclear power plant. To pump enough water, continuously, to irrigate 9 million km2, potentially feeding a billion people, once we dig swales! (Check out Africa’s better-than-trees plan: “Demi-Lune” swales that catch sparse, seasonal rain, to seep into the ground, with minimal tools and labor!)
Yes, as I mentioned twice now:
The reason there is a desert is because the Hadley and Ferrel Cells are meeting and descending along the Horse Latitudes. As that air falls from 10km up, it compresses, which causes adiabatic heating. And, at that initial altitude, it only contained 0.1g water per m3 to begin with—so, as that air reaches the ground, hot and dry, it sucks-up all the humidity, keeping the air below the threshold for making rain.
We know as a geological fact that the amount of water being sucked-up by that adiabatic heating is only a little bit more than the amount of water that the seas are evaporating. This is because, only a few thousand years ago (and in cycles repeatedly) the entire Sahara was green, due to a slight increase in evaporate and sea-breeze due to increased convection. It was only a SLIGHT increase which allowed the humidity to cross that threshold of rain-cloud formation, leading to an accumulation of moisture, plant life, driving more convection in a feedback loop that brought lakes to the Sahara. You seem to ignore the fact that the whole Sahara was green!
So, we only need to add enough additional humidity to cross the threshold of clouds, before all further evaporate becomes rain, in surplus. I’ve explained this a few times now. Are you noticing the details I point out, most of all “crossing a threshold of adiabatic desiccation”?
Ok, so that’s the important detail I missed. A small amount of extra moisture would cause all the existing moisture to rain down.
Do we have any way of knowing how much extra, or where?
Erm, no, still a mistake. Let’s walk through a different format:
You have a bank account, which is auto-billed $3million a day by adiabatic downdrafts, so you are nervous about making that payment every day—especially because you are only evaporating $2million a day to add humidity to your account! You’re going $1million into debt, daily. That’s a desert.
Yet, the Sahara got 10% more sea-breeze convection, 11,000 years ago, which was enough for it to have a budget surplus—that’s like saying “Sahara’s account is being billed $3mill a day, and they were previously only able to put-in $2.9mill a day, but now Sahara is earning 10% more sea-breeze, which puts daily earnings at $3.19mill, for a surplus of $190K a day—Sahara will start forming lakes, now!” And that plant life it gets will pull more sea-breeze in a feedback, to help-out.
So, the added moisture is NOT causing “all the existing moisture to rain down.” It’s about exceeding the threshold, to generate a surplus. And we know, from Sahara’s green periods, that the desert is actually pretty close to that surplus—Sahara needed only 7% more sunlight, to drive 10% more wind!
Ok, got it now. Still, is there any way of knowing how much that is? 10% of all the water evaporating from all the seas near the Sahara is still a huge amount of water. And if we do add more water, is there any way of knowing where it will rain down, as opposed to being spread over the entirety of the Sahara and ending up basically useless?
Or is this the sort of thing where you would have to invest huge amounts into infrastructure to do this, before you can tell what affect it will have?
How quickly it rains down depends on a few factors, and we can tip those in our favor:
--> Humid Rise—humidity (just the h2o molecule) is only 18g/mol, while oxygen molecules are 32g/mol, so humid air is quite buoyant! Especially considering that water vapor reflects heat (infrared) back to the ground, creating a heat bulge beneath it. The result is that, once humidity begins to rise, it naturally pulls air in from all around it, along the ground. It begins to drive convection. Yet! That humid rise is normally billowy and easily dispersed by cross-breezes, which means that the humidity cannot rise high quickly; it mostly travels far overland, or stays in place. Your rain wanders to an unexpected location! We want to form rain clouds nearby, instead, so we need that humidity to rise really high, quickly, without being torn apart by cross-breezes. That’s where the solar concentrators help, with their tall tower at 1200C and radiant, they blast infrared into all the water vapor around them, pummeling a plume high up, carrying that vapor. Up high enough, the air pressure drops, which is key for causing a rapid cooling, and the formation of nice heavy clouds. The faster we take air from the ground up to a few kilometers, the more water it’ll still be holding. [[Only a fraction of one gram per m3 is needed for the thinnest clouds, but we could toss a few grams up and it’ll come down soon. We want the water to rain, evaporate, and rain down again, in as many cycles as it can. That gives plants time to grab it, in numerous locations, as well as time for the ground to catch some.]] When we look at water-demand for plants in the wild vs. water-resilient greenhouses, we can drop water demand ten-fold because nine-tenths of the water was lost in the leaves to evapotranspiration! As a result, if that leaf-sweat keeps rising and falling as rain as it travels further South, then the same bucket of water ends up getting ten times the use (assuming ground water is eventually used, as well).
--> Albedo—the desert rock is pretty bright, so the addition of vegetation and especially any water-bodies (!) will multiply the solar absorption, which will drive that heat-bulge and evaporation for humidity-buoyancy, to help loft water vapor and form clouds. This is how the Amazon does it—most of her clouds are her armpit fog, caused by solar-to-thermal foliage!
--> Vortices—the solar concentrators themselves can be rigged with a few flanges, to nudge their inflowing convection as it quickens toward the center, to spin that up-draft, helping it stay coherent and push higher, for rains nearby. Any Youtube video on Rocket Stoves by Robert Murray-Smith is best for enjoying such a vortex!
--> Swales—I love swales. I’ve been preaching swales since 2010. I heard, almost immediately, when Sepp Holzer started pitching his “crater gardens” … which were dug by an excavator, four feet deep. I was aghast—my favorite swales are micro-swales, a few inches deep, in flakey soils that rain seasonally, to catch it as it dribbles. That’s what they’re doing in the Sahel, south of Sahara, to stop the deserts. By halting the flow of water along the ground, keeping it for seep, roots, and another evaporation, you prolong the residence-time of each ton of water, leading to a greater equilibrium stock—that is, a high normal lake line, because each ton of water rarely ever leaves.
And, as to infrastructure before success—California could probably boost rains enough to help farmers and forests, here, without needing to conquer an entire desert the size of Europe!
Thank you for diving into the details with me, and continuing to ask probing questions!
The water brought-in by the Sahara doesn’t depend upon the area of the source; it’s the humidity times the m3 per second arriving. Humidity is low on arrival, reaching only 50% right now in Tunisia, their winter drizzles! The wind speed is roughly 2m/sec coming in from the sea, which is only 172,800m/day of drift. Yet! That sea-breeze is a wall of air a half kilometer high—that is why it can hold quite a bit.
If we need +10% of a 500m tall drift, that’s 50m; if we can use solar concentrators to accelerate convection, we can get away with less. And, we’re allowed to do an initial row that follows the shoreline closely, while a second row is a quarter kilometer inland, running parallel to the shore, where mixing of air lets you add another round of evaporate. So, we could have four rows across the northern edge of the Sahara, each row as thick as it needs to be to hit high humidity, and 10m tall, to send +10% moisture over the entire 9 million km2 of the Sahara.
How much water would we be pumping? The Sahara carries 172,800m/day flow per m2 intake surface x 500m tall x 4,000km coastline at 10g h2o per m3 = 3.5 billion tons per day, a thousand or so dead seas. (About 1.25 Trillion tons a year, enough to cover the 9 Million km2 with 139mm of rain, on average, if it had fallen instead of being sopped-up by adiabatic heat.)
We need 10% of that, or a hundred and eighty dead seas. It seems monstrous, but much of the coastline there is low for miles, so pumping 1 ton to the top of 10m at even just 20% efficiency costs 500kJ. If you want to pump that in a day, using solar, you’ll need 1/4th of a square foot of solar. That 1 ton, if we cross the threshold and it becomes surplus rain, will water 3 square meters their annual budget… and the solar is paying for that amount of irrigation every day; 1,000 m2 of rains from a dinner plate of solar, each year. It’s that energy efficiency, combined with dead simple capital expenditures, which would make something so insane potentially feasible. I’d pick California to try, first!
500kJ per ton, for 350Mil tons per day—that’s 175TJ per day, or 2 GW. That’s a nuclear power plant. To pump enough water, continuously, to irrigate 9 million km2, potentially feeding a billion people, once we dig swales! (Check out Africa’s better-than-trees plan: “Demi-Lune” swales that catch sparse, seasonal rain, to seep into the ground, with minimal tools and labor!)