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
[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 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 --- Alan Gadian, NCAS, UK, ( sent from a mobile device ) Email:
[email protected] or [email protected]
Tel: +44 / 0 775 451 9009 or +44 / 0 113 343 7246
T ---
On 31 Dec 2014, at 23:46, Rob Wood <[email protected]> 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).
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), 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
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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