Thursday, February 23, 2017

Are cool roofs reducing rainfall and increasing pollution?

Are cool roof paints reducing rainfall? 
Regarding pollution, says, 
"The lowered wind speeds and vertical mixing during daytime led to stagnation of air near the surface, potentially causing air quality issues." 
Why not distribute a solar air heater that can be attached to roofs? The solar air heaters will shade roofs during the day and heat air, but also be cooled by the air passing through. This should cause cloud formation which will keep the city warm at night.  Paint manufacturers could team up with solar air heater manufacturers to produce this air heating, roof cooling and rain enhancing solar air heater on roofs situation.
See for information on solar air heaters.
Drought in coastal cities: I am wondering if it would not be better to make buildings in, say, Los Angeles a dark colour to heat up more and enhance chances of rain (or use solar air heaters on roofs as mentioned above). One hears about a 10% increase in rainfall due to urban heat island effect. I have done some calculations:
Assume the air from the sea has a relative humidity (RH) of 70% and is at 18 deg C and it blows onto land and heats up over the city, but remains at 18 deg C over the rest of the area (a simplification to make calculations easier). My calculations use an environmental lapse rate of 6.5 deg C per km rise and a dry adiabatic lapse rate of 9.8 deg C per km rise. The dew point of the sea and land air remains at 12.5 deg C whether heated or not, but the RH changes on the air being heated. My calculations show the number of degrees the air heats up over the city (1 deg means it heats up to 19 deg C from the 18 deg sea air temperature). Then they show the change in RH of the air after heating. Then they show the height to which the heated air can rise and the height to which it needs to rise for clouds to form: 0) Heats up 0 deg over city, RH remains 70%, the air can rise 0 m and it needs to rise 694 m for clouds to form. 1) Heats up 1 deg over city, RH is now 65.8%, the air can rise 303 m and it needs to rise 819 m for clouds to form 2) Heats up 2 deg over city, RH is now 61.8%, the air can rise 606 m and it needs to rise 944 m for clouds to form 3) Air heats up 3 deg over city RH is now 58.1%, the air can rise 909 m and it needs to rise 1069 m for clouds to form 4) Air heats up 4 deg over city RH is now 54.6%, the air can rise 1212 m and it needs to rise 1194 m for clouds to form 5) Air heats up 5 deg over city RH is now 51.4%, the air can rise 1515 m and it needs to rise 1319 m for clouds to form 6) Air heats up 6 deg over city RH is now 48.4%, the air can rise 1818 m and it needs to rise 1444 m for clouds to form After step 4 the air is heated enough for clouds to form - see the graph. Note that more cloud formation could cool Earth overall.
Here is another very good design to get air moving upwards:

See which says, "However, they shift rainfall patterns by reducing evapotranspiration, the process by which water evaporates from the ground and enters the atmosphere. In the maximum expansion scenario, cool roofs led to a 4 percent decline in rainfall."
One could increase convection by using solar air heaters made by placing a black piece of corrugated iron roof sheet a few centimetres above a silver sheet of corrugated iron. Another method is to make the soil dark with biochar - plow biochar into the soil. You can make your own biochar by heating wood in a barrel. 
You can also paint rocks black: Rocks have a high heat capacity - they hold a lot of heat. If cool roofs reduce rainfall, rocks painted black can increase rainfall. 
Just as cool colours can decrease rainfall, so can dark colours incease rainfall by increasing convection. See
When clouds develop, because of convection, they will help with global warming by cooling the Earth. 

Friday, February 17, 2017

Cool Arctic with heat pipes

Heat pipes are used in the Arctic to keep the ground cold so that structures are secure. The heat pipe, used next to the structure, uses a fluid that is heated in winter by ground temperatures that are higher than the air temperatures. The fluid evaporates, moves up from the ground into the air zone and condenses into liquid, releasing the heat to the cold air. This liquid now moves downwards and the cycle starts again - see thermosyphons section at
Now part of the reason that there is little snowfall in the Arctic is that with thawing and evaporation in summer there is relatively a lot of moisture in the air, but the air is cold (so cannot hold much moisture) and does not rise far enough to cause snow to fall (it needs to be warm so it can rise and cool significantly so that a lot of water vapour condenses out). The thermosyphon warms the air and cools the ground, so there are two benefits. A solar air heater could be used above the thermosyphon so that cool air is drawn in from ground level to cool the top of the thermosyphon. This will dramatically increase the ability of the air to rise far and cause snowfall. Snowfall increases the albedo and so more cooling will occur.
If you put a 1 sq metre solar air heater above the thermosyphon on a clear day at noon on 1 July at the latitude shown on the graph, you can theoretically heat the number of cubic metres of air shown by 1 deg every second. This is for a "facing the sun" solar air heater. A horizontal solar air heater at these latitudes gets much less insolation. There are two important aspects at these latitudes: 1) the amount of air the sun shines through 2) the angle of the solar heater. Both these have been taken into consideration in the calculations.

Thursday, February 9, 2017

Clean water from seawater and Arctic clouds

People are worried about heating of Arctic regions. In winter the ice can reflect solar energy and cool Arctic regions, but in summer clouds can reflect solar energy in regions where ice has melted (however increased humidity can increase the greenhouse effect). 
One of my "inventions" that could increase the relative humidity (and therefore clouds) is being investigated by a university of technology in South Africa. It could be used for drought areas. 
One can dramatically increase relative humidity by adding water to the air.
Calculations for air at 25 deg C: At a 50% relative humidity in a column of air of base of 1 sq metre and height of 1000 m (1000 cubic metre column) there are 11.5 kg of water vapour. In the same column with an RH of 90% there are 20.7 litres of water vapour. If you can add 20.7-11.5 = 9.2 litres you can therefore increase the RH from 50% to 90%. You need 9.2/1.6 = 5.75 kWh to do this (theoretically, since 1 kWh can evaporate 1.6 litres of water). In a day 5.75 kWh of solar energy can fall on the 1 sq metre base of the column in some regions. With higher RH clouds can form more easily. 

See also my diagram for clean water from seawater. This apparatus could be used to increase humidity of the surroundings if it was used on every rooftop. Note that the idea is similar to the idea of a solar updraft tower with hot air rising, due to natural convection, through the system. Black mesh or gauze could be put into the greenhouse to give a large moist surface for hot air from the solar air heater to blow over. See gives some cloud physics and tells how to spread snow evenly using windbreaks. Snow increases albedo keeping an area cool.
I do not intend to patent my clean water from seawater device, because it is intended to help everybody and I hope people start building it for themselves.

 Here is how you can work out relative humidity problems for yourself: You can use the table at When relative humidity is 50% and temperature is 25 deg (see table) you find that there are 11.5 g/cubic metre of water vapour (this is the same as 11.5 kg per 1000 cubic metres). Likewise there are 20.7 kg of water vapour per 1000 cubic metres when RH is 90% (see my example above). says
"The effect of a thin snow cover is dramatic, particularly in the NIR. Just 5–10 mm of continuous snow cover raised the broadband albedo from 0.49 to 0.81, nearly as high as values measured for deep snow on the Antarctic Plateau, α = 0.83" and "Wind often cleared the snow from the ice. On one occasion a new snowfall of 2–3 cm raised the albedo from 0.42 to 0.88, and on another occasion a snowfall of 1–2 cm raised the albedo from 0.39 to 0.78."
So my idea is to have windbreaks in the Arctic that spread snow evenly and prevent it from blowing away.
My Calculations on Arctic ice/snow, using equations from Fundamentals of Thermal-Fluid Sciences by Cengel and Turner: 
1) Assume solar radiation (direct and diffuse) on snow or ice is 500 W/square metre. 
2) Assume emissivity of snow or ice is 0.97.
3) Assume absorptivity of snow or ice changes from 0.6 to 0.2 when snow falls (albedo increases when snow falls and absorptivity decreases).
4) Assume the effective sky temperature is -20 deg C
5) Assume temperature of ice or snow is -5 deg C.
Then for absorptivity of 0.6 (low albedo) the ice/snow has a heat gain of 242 watts per square metre. For an absorptivity of 0.2 (high albedo) the ice/snow absorbs only 42 watts per square metre. says, "Because the Arctic Ocean is mostly covered by ice and surrounded by land, precipitation is relatively rare. Snowfall tends to be low, except near the ice edge. Antarctica, however, is entirely surrounded by ocean, so moisture is more readily available. Antarctic sea ice tends to be covered by thicker snow, which may accumulate to the point that the weight of snow pushes the ice below sea level, causing the snow to become flooded by salty ocean waters."

Saturday, February 4, 2017

Rain from temperature differences.

I was reading
which says, "Such a large acceleration arising from only a modest temperature difference illustrates the importance of buoyancy in determining vertical transport in the atmosphere."
I am convinced that having lighter coloured areas round a city with a dark area in the middle one could get air rising fast and possibly get rain to fall when the air cools higher up. Example: The black inner area heats up 3 deg C more than the surrounding lighter coloured surroundings (very feasible) to say 30 deg C (surroundings at 27 deg C). Then this hotter air mass initially accelerates from the ground at about 0.1 m/s^2.
Later on, within a cloud formation, if there is a 3 deg C temperature difference, the hotter air can reach an upward velocity of about 9 m/s relative to the rest of the cloud (using an equation from a cloud physics text). On getting colder this rising air mass will cause more condensation. Could we use some fairly harmless dye to darken areas of the sea so that temperature of the dark area is one or two degrees higher than the surroundings and so cause rain. Could plankton be used to darken an area?
See also