Hi All
The words 'charge' and 'electrostatic' do not appear in Stuart et
2013. People cleaning oil tanks in the 1960's found the painful way
that its is difficult NOT to generate charge, see
http://www.infostatic.co.uk/Papers/TankWashingRisks.pdf . There are at
least two ways by which we can control charge.
The Stuart paper used a size distribution of 100 size bins, spaced
logarithmically between 10 nm and 10 μm in wet diameter rather than
mono-disperse spray. This is a range of 1000:1. I hope to keep within
20%. Coagulation requires a relative velocity between drops. Viscous
forces are very large at sub-micron dimension. Particles will behave
like sand in honey. Small scale turbulence will tend to vary the
velocity of particles but while the Stokes drag force goes with the
first power of diameter the mass resisting acceleration goes with the
cube. If there is a wide range of drop diameters, local turbulence will
produce much larger range of relative velocities. It would be useful to
know coagulation rates for narrow ranges of drop diameter.
In my paper on the detection of small contrast changes I assumed a loss
of 50% which would not be a show stopper.
In figure 2 of of the Stuart paper there is no sign of any initial drop
due to evaporative cooling.
Stephen
Emeritus Professor of Engineering Design. School of Engineering.
University of Edinburgh. Mayfield Road. Edinburgh EH9 3JL. Scotland
s.sal...@ed.ac.uk Tel +44 (0)131 650 5704 Cell 07795 203 195
WWW.see.ed.ac.uk/~shs YouTube Jamie Taylor Power for Change
On 01/01/2015 02:48, Alan Gadian wrote:
Rob,
I agree here with you. With LEM modelling with WRF Chem, the bdy
layer schemes can be very diffusive. Ignoring the electrostatics
charge element, I am concerned that the PDFs of the vertical
velocities are critical. From experience 20m is not good enough
resolution in the vertical. How does the model cope with changes in
cloud droplet number, as seen in andrejczuk (2012 aNd 2014) . The
vocals profiles provide data on the BL dynamical profiles, and I fear
with the wef chem LEM results, the dynamics and hence the dispersion
are inadequately represented. WRF Chem is about 20 times slower than
WRF without the chemistry package, and thus the representation of the
dynamics has to be compromised for the inclusion of the chemistry. I
would like it clarified about how these results compare with
observations.
The papers of Andrejcuck provide a surprisingly efficient and rapid
dispersion, and compare reasonably well with observations.
Alan
T ---
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On 31 Dec 2014, at 23:46, Rob Wood <bobbywood2...@gmail.com
<mailto:bobbywood2...@gmail.com>> wrote:
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
s.sal...@ed.ac.uk 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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