ship tracks
Andrew Lockley
Here’s the ship tracks presentation abstract from IUGG which I
particularly recommend, plus two other abstracts on the subject. I
hope to be able to send the presentation in due course, but don’t
currently have access. Below are also two other abstracts on the
matter which may be of interest
A
D Rosenfeld 1 Can We Afford Curbing Ship Tracks by Banning Bunker
Fuel: An Unplanned Global Scale Experiment in Geoengineering
A method for tracking overnight the evolution of ship tracks that
close open cellular
marine stratocumulus shows that negative radiative forcing due to such
ship tracks may
greatly exceed previous estimates. At times exceeding 36 hours the
ship tracks were
observed to expand to width exceeding 200 km, and lose their linear
appearance. Large
areas of closed marine stratocumulus were related this way to be
induced by ship
emissions in previous days. The added radiative forcing of such
clouds, which is mainly
coming from the cloud cover effect, is in the order of -50 to -100
wm-2, depending on the
season and latitude. This means that the aerosol cloud mediated
negative raditive forcing
from marine stratocumulus is likely much larger than estimated until
now. This is probably
compensated by positive cloud radiative forcing induced by aerosol
invigorating deep
tropical clouds and enhancing the cirrus outflow from their anvils,
which has been also
under-appreciated until now.
The International Maritime Organization (IMO) Marine Environment
Protection Committee
(MEPC) announced April 4 2008 that it has approved proposed Marpol Annex-6
amendments to require heavy bunker fuel sulfur limits to fall to 0.5%
by 2020. The ship
bunker fuel limit initially will drop from today's 4.5% sulfur limit
to 3.5% starting Jan. 1,
2012. Given the findings described above, this means a large
reduction of the cooling
effect by ship emissions. This is in fact an uncontrolled experiment
in geoengineering,
which will probably contribute to global warming in unknown ways and
unpredictable
consequences.
http://www.sciencedirect.com/science/article/pii/S0169809509002373
Observations of the instrument SEVIRI (Spinning Enhanced Visible and
Infra-Red Imager) onboard the geostationary orbit Meteosat-8 were
analyzed to study the diurnal behaviour, length and lifetime of
so-called ship tracks near the west coast of southern Africa. Several
days of data between May and November 2004 from the SEVIRI 3.9
µm-channel were used to analyse the characteristics of more than 230
ship tracks by visual analysis. The results show a diurnal variation
with maximum occurrence around 10 am. The length and lifetime of the
230 ship tracks shows significant variation: the mean lifetime
detected by means of the visibility in the 3.9 µm channel, was 18 h (±
11 h), but lifetimes up to 60 h have also been observed. The mean
observed length is 458 km (± 317 km), with an observed maximum of 1500
km, showing a high dependence on wind direction in the region of
interest. To take into account the high variations of the examined
variables, we also present distribution functions for the length and
the lifetime of ship tracks. The distribution functions can be used to
improve estimates of radiative forcing from polar orbiting satellites
and for parameterisations of sub-grid scale processes in global model
simulations.
http://www.see.ed.ac.uk/~shs/Climate%20change/Data%20sources/Schrier%20ship%20track.pdf
Global ship track distribution and radiative forcing from 1 year of
AATSR data
[1] One year of ENVISAT-AATSR (Advanced Along
Track Scanning Radiometer) satellite data is analyzed to
derive a global distribution of ship tracks and their radiative
forcing (RF). Ship tracks are changes in cloud reflectance,
visible in satellite data, and result from the emission of
aerosols and their precursors by ships into the clean marine
boundary layer. An algorithm is presented that extracts
scenes dominated by low clouds over the oceans that are
susceptible to be affected by ship emissions. These selected
cloud scenes are used to examine ship tracks on a global
scale via visual analysis. The results show a high temporal
variability of ship track occurrence with peak values in July.
They also show a high spatial variability with peak values in
the North Pacific Ocean and on the west coast of southern
Africa, correlated with high ship traffic and frequent low
cloud occurrence in regions of cold upwelling ocean
currents. The analysis of backscattered radiation at top of
the atmosphere (TOA) compared to the surrounding area
reveals enhanced backscattering with values between 0 and
100 Wm
2
. For particular regions on the west coast of
North America, the annual mean RF due to ship tracks
estimated by the changes in backscattered radiation at TOA
can be up to 50 mWm
2
. The global annual mean RF due
to ship tracks is small ( 0.4 to 0.6 mWm
2
) and
negligible compared to previous global model estimates
on the total indirect aerosol effect and RF contributions
of other ship emissions. Citation: Schreier, M., H. Mannstein,
V. Eyring, and H. Bovensmann (2007), Global ship track
distribution and radiative forcing from 1 year of AATSR data,
Andrew Lockley
Link to papers on the subject, which I just received from the lab.
A
http://dl.dropbox.com/u/13587617/ShipTracks.rar