Misconceptions about hydrosols and NPP

[Russell Seitz]

Andrew wrote    On Sunday, April 23, 2017 at 9:40:00 PM UTC-4:

I don't think hydrosols will behave like CNN, in terms of their radiative properties. As I understand it, CCN act to brighten existing cloud cover. They won't, therefore, work on cloudless days. Likely, relative efficacy will depend on whether acute or chronic thermal stress is most important. Furthermore, hydrosols will cause a lasting increase in diffuse radiation. In terrestrial models, this has impacted NPP.

I'm no expert on this niche - but that's my initial thoughts.

Hope it helps

It will take field experiments and further modeling  to quantify  the Net Photosynthetic Product  impact  of surface water brightening , but Andrew should bear three things in mind

1. Backscattering light does not have the  same effect  as casting shade, because most plankton  and algae can absorb light in all directions, 

2.  Hydrosols scatter the infalling light in all directions,  - they change  the geometry of the euphotic zone in a diffferent manner than  extensive cloud cover.

3. Doubling surface brightess at high sun angles , from  ~ 7%  to 14% reduces the underwater light flux  by about 7%, which while obviously significant, is a small reduction relative to  full cloud cover, which  often reduces  surface light  more than twice as much, as white clouds in the air can have an albedo of up to .55.- m

It may l accordingly  take as much   NPP research to  sort out the ecological meaning of the  physically uncontroversial cloudy day analogy  as that of CCN shading of overheated seas , both triopical and  circumpolar.

[Stephen Salter]

Hi all

The change from an untreated cloud to a treated one is much smaller than that from a cloud to clear sky let alone day to night. The contrast change needed to offset double CO2 with 18% low cloud cover is well below the detection threshold of a human eye. 

Stephen

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[Russell Seitz]

Thank you Stephen- 

I've posted a  very brief ( under 4 minute ) < a href ="https://www.youtube.com/watch?v=y-0RRDf8vAI"> slideshow  illustrating some of these points:

https://www.youtube.com/watch?v=y-0RRDf8vAI</a>