Dear All,
I think that some degree of coagulation given such localized point
sources of large numbers of particles is inevitable, as shown in the
paper by Stuart et al. (2013)
<http://www.atmos-chem-phys.net/13/10385/2013/acp-13-10385-2013.html>.
This will also be the case with charged particles. Nevertheless, I don't
think that this is necessarily a fundamental limitation. After all,
shiptrack formation, where even larger numbers of particles are
produced, still occurs. Coagulation must be considered in the
calculations. That said, in our recent paper (Connolly et al. 2014
<http://faculty.washington.edu/robwood2/wordpress/wp-content/uploads/2014/06/Connolly_etal_PHILTRANS_2014.pdf>),
we found significant albedo enhancement in a parcel model even with
quite broad size distributions. The optimal median particle size becomes
smaller as the size distribution spread broadens (e.g. from
coagulation). For broader distributions typical of those produced in lab
tests, the optimal median droplet diameters need to be somewhat smaller
than 0.1 micron.
I tend to agree with Stephen that near-surface spreading due to initial
negative buoyancy from evaporation of water from the small seawater
droplets may not necessarily be a tremendous problem for the reasons he
states. This has not yet been considered in any model that I know of,
but could easily be done with large eddy models.
Rob Wood
On 12/30/2014 8:35 AM, Stephen Salter wrote:
Hi All
Piers Forster's concern in his video about spray coagulation would be
reduced if his model had used mono-disperse drops with an
electrostatic charge as specified in our 2008 paper on sea-going
hardware.
His concern about detecting the effectiveness is because the cloud
contrast change needed to save humanity is below the detection
threshold of the human eye. However contrast can be enhanced by the
superposition of satellite aligned images. I have previously
circulated some to this group and hope that the idea will give
quantitative results in a few days.
The picture of spray plumes shown in box 3 of his IAGP practicalities
note must have been using warm air from a chimney. Depending on the
temperature and relative humidity of the surrounding ambient air there
will be several degrees of temperature drop due to the latent heat of
evaporation. The increase of density will lead to a rapid fall of the
cooled air which will spread out over the sea surface like a spilt
liquid until it has been warmed by the large area of contact with sea.
You can show this fall and dispersion very cheaply with a pond fogger,
£19.99 from Maplin. We want this dispersion because a low dose over a
large area is more effective than a high point dose.
Forster seems to be ignoring completely the idea of coded modulation
of CCN concentration in climate models even though the satisfactory
operation was demonstrated by Ben Parkes doing a PhD in Forster's own
Department at Leeds in 2012. This might allow us to get an
everywhere-to-everywhere transfer function of marine cloud brightening
and win-win result with more rain in dry places and less in wet. The
high frequency response means that we can give a tactical spraying
based local day-to-day observations.
It is a puzzle that the Parkes thesis has, yet again, vanished from
the Leeds University website.
Stephen
Emeritus Professor of Engineering Design. School of Engineering.
University of Edinburgh. Mayfield Road. Edinburgh EH9 3JL. Scotland
[email protected] Tel +44 (0)131 650 5704 Cell 07795 203 195
WWW.see.ed.ac.uk/~shs YouTube Jamie Taylor Power for Change
On 28/12/2014 20:03, Andrew Lockley wrote:
Integrated Assessment of Geoengineering
Proposals…:http://youtu.be/FFjzzfCLCqw <http://youtu.be/FFjzzfCLCqw>
Poster's note : I personally have found it very difficult to access
and appraise the science behind the IAGP project. Despite this, a
vast amount of publicity has been obtained for the project. I think
the IAGP team could do more to encourage early, in-depth access to
their material, particularly bearing in mind the huge media interest.
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