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Sun to Rain

Redirect sun to increase rainfall in California
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This may be applicable elsewhere, but California definitely has the right conditions:

Put a huge solar diffuse solar mirror in geostationary orbit over the desert southwest. This mirror intercepts say maybe 10% of the sunlight that would otherwise fall on this area. A lot of energy, but not enough to shade any one area completely.

This sunlight is not blocked, but redirected slightly to a patch of ocean somewhere off the coast of California. That portion of the ocean warms, increasing the evaporation. The correct level of concentration is to be determined, but I'm thinking you'd only want to increase total insolation by a factor of 1.1-1.2, so it could be close to 1:1.

At the same time, the desert southwest cools, producing a low pressure area. This causes the extra moisture to be sucked in from the ocean and over California, increasing rainfall.

(And yes, I know there are massive issues with potentially warming the oceans, and killing wildlife, and so on. Deal)

MechE, Mar 23 2015

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       How does a geostationary orbit that isn't above the equator work?
scad mientist, Mar 23 2015
  

       I'll be honest, I didn't think this idea out that much, but...   

       You cheat. You use a geostationary altitude that moves north and south of the equator by the lattitude of your northernmost point, and is at the peak around noon. That leaves it in the target area for a significant chunk of the daylight (and maybe you increase the intercepted light to offset the decreased time). Also you possibly play with an elliptical orbit such that you've got a slightly longer, slower portion in the daylight. Details to be worked out if I find something that lets me model orbits easily.
MechE, Mar 23 2015
  

       Another question to refine this... When you redirect the light to the ocean, is there any advantage to keeping it concentrated? Even if you spread the light over a larger area than you are shadowing, all that solar energy still goes into the water. It seems like it would be linear up until you got the water hot enough to start bubbling. Speaking of which, you could make an offshore concentrated solar generator if you made the reflectors accurate enough.
scad mientist, Mar 24 2015
  

       I'm really not sure on the concentration. It feels like some would be desirable, just from a controlling where the energy goes standpoint, but it may not be needed.   

       Concentrated solar from orbit requires very concentrated sunlight, and suffers from atmospheric distortion, so you're going to have your plant generating power, and boiled fish around it.
MechE, Mar 24 2015
  

       All other considerations aside, if you focused your efforts far enough offshore, you'd kill a minimum of fish - they tend to collect near structures and shallows, with some exceptions of course.   

       And after the initial heatup, they'd learn where not to hang out. This would of course affect currents, which affects feeding and other phenoms.
normzone, Mar 24 2015
  

       Hmmm... I think there's a problem here. Unless we're doing one of those biblical "the sun was standing still" things, it seems like the the shadow is going to be headed that-a-way (points off in direction of lessening longitude)... OK. Calculator out.   

       I look at my little diagram which represents the earth, the sun (in this reference frame, stationary at the top of the diagram) and the mirror array (travelling around the earth in 24 hours, give or take a few minutes of siderialness).
Geosync orbit radius = 42,164 km (you think, "that's not right!" - but the number you're more used to seeing is altitude above earth's surface, which is not of interest here)
Distance moved by mirror array in 24 hours: 0 km (oops, useless result, it went back to where it started from)
Distance moved by mirror array in 12 hours: 84,328 km (the sun sees it moving back and forth along a line, not around in a circle)
Average speed of eastbound shadow: 84,328km/12hr => 7,027 km/hr
Since that's the average of a sinusoidal curve, peak velocity (which will hit at precisely the point you'd rather have it stationary) will be 7,027 * sqrt(2) = 9,938 km/hr.
Just slightly over Mach 8. I'm thinking that could be an issue. ;)
lurch, Mar 24 2015
  

       What [lurch] said. Plus, unless you're controlling the angle of the mirror, the hot spot is going to travel, too, as the angle between the sun's rays and the mirror changes due to the mirror's orbit.
the porpoise, Mar 24 2015
  

       //is there any advantage to keeping it concentrated?//   

       Ultimately, this is just a heat engine. So, you'll get the most bang for your bucks if you keep the hot side as hot (and therefore as concentrated) as possible.
MaxwellBuchanan, Mar 24 2015
  

       I was definitely figuring on a controllable mirror array.   

       Lots of little mirrors, each with a driving motor. This also allows for correction of the aiming point for the north/south wandering, and adjustments to where the rain forms relative to the points that need it most.   

       Yeah, the shade is going to drift, but you've got it overhead when it's in the desert, anyway. And once again, an elliptical orbit might allow you to improve that a bit by causing the mirror array to apparently drift backward and forward over the earth, but I still haven't found a way to simulate that.   

       After some quick math, however, it looks like the mirror array will only shade the earth at all for about an hour each day. After that, you're missing to either side. Which sort of defeats the advantage of producing the desired low pressure area (and the unstated desire to keep the total idea insolation neutral).   

       Which means the idea might work better as a constellation of LEO arrays. More expensive to build, cheaper to launch.
MechE, Mar 24 2015
  

       I think you need to beat the cost of desalinization plants. How about large tethered balloons with cleverly designed reflective surfaces?
the porpoise, Mar 24 2015
  

       I think this is achievable on a much larger scale than de-sal plants, and the operating cost is essentially zero once the plant cost is dealt with, unlike de-sal.
MechE, Mar 24 2015
  

       Water already costs more than gasoline. Why don't they just start mining antarctic glaciers. They can simultaneously fix the drought and reduce worry about rising sea levels. Not to mention opening up an entire continent.
theircompetitor, Mar 24 2015
  

       Plankton and other green things would surely grow more.   

       ( We have had unusual winter rains locally in San Diego. A second generation of weeds when usually only one by now. Gophers and other things that eat weeds have had population explosions. Now knee deep in weeds that are shading out and killing the ice plant. The ice plant is one of the few that can survive the hot dry summer. Looking forward to barren hills due to critters and shading. Kinda of ironic.)   

       Just cranking up one major variable in an ecosystem, is not magically going to make it all come up roses.   

       (Speaking of roses...)
popbottle, Mar 24 2015
  

       This should make for a healthy raptor population this year.
normzone, Mar 24 2015
  

       // Water already costs more than gasoline // You're talking bottled water. That costs about 2000 times as much as tap water according to Google. Of course that utility price is probably regulated which is why it has to be rationed.
scad mientist, Mar 24 2015
  

       And if it wasn't regulated, people in the US wouldn't eat so well. California exports water to the rest of the world one tomato, one head of lettuce, or one orange at a time.
MechE, Mar 24 2015
  

       Perhaps California should just require all exports to be dehydrated.
lurch, Mar 24 2015
  

       //Perhaps California should just require all exports to be dehydrated//   

       All the grape juice I import form California is dehydrated by 10-13%.
bs0u0155, Mar 24 2015
  

       [lurch], that's displacement.   

       A possible improvement: Two satellites. The first reflects the sunlight to the side (or back up at an angle) and the second down to the ocean. That eliminates the necessity for a mirror much larger than the area*amount that it shades because it has to be so oblique.
notexactly, Mar 25 2015
  
      
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