Presentation - Magdalena Anguelova
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Transcript Presentation - Magdalena Anguelova
Novel Applications of Remote Sensing
for Improved Quantification of
Sea Spray Source Function
Magdalena D. Anguelova
Michael H. Bettenhausen
William F. Johnston*
Peter W. Gaiser
Remote Sensing Division,
Naval Research Laboratory, Washington, DC
* Computational Physics, Inc., Springfield, VA
Motivation
Whitecaps
Gas exchange
Ocean albedo & roughness
Geophysical retrievals
Dominate the activation of CCN
Sea spray aerosols
Direct effect – cooling
Indirect effect
Halogen chemistry
Reactive Cl and Br
Tropospheric O3
Sink of S
Surface wind
Ocean color
Salinity
Sea spray droplets
Heat exchange
Tropical storm intensification
6 Dec, 2011
Whitecaps and sea spray, Anguelova et al., NRL
Photo courtesy of C. Fairall
Compete with SO42- aerosols
2
Sea spray source function
Rate of production of sea spray per unit area per increment
of droplet radius, r (s-1 m-2 m-1).
dF (r , a, b,... )
= f(U ) f( r )
dr
Scaling factor Size distribution
Magnitude
Shape
-6
3.41
=
f (U ) W (U10 ) 3.8 10 U10
From photographic
measurements
(Monahan and O’Muircheartaigh, 1980)
f (r80 )
d
f (r )
d log10 r80
6 Dec, 2011
From measurements using
various methods
Whitecaps and sea spray, Anguelova et al., NRL
3
Possible improvements
For the size distribution f(r)
Extend the size range, large and small ends
1 μm < r80 < 25 μm
de Leeuw et al.
O’Dowd et al.
Keene et al.
Quinn & Bates et al.
Meskhidze & Peters et al.
0.1 μm < r80 < 250 μm
Recognize and include the effect of organics
Introduce ambient factors f (r) f ( r , a , b ...)
(de Leeuw et al., 2011)
Ernie Lewis poster
Sofiev et al., 2011
For the scaling factor f(U)
Less uncertainty in measuring W
Introduce ambient factors W (U ) W (U , a , b ...)
Remote sensing: method, results, implications
6 Dec, 2011
Whitecaps and sea spray, Anguelova et al., NRL
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Objective
Measure W globally
Compile database
Model the high variability of whitecap fraction
W (U )
W (U , T , X , d ,U cur , Ts , S , C)
U – wind speed (U10 or u*)
T – atmospheric stability (= Tair – Tsea)
X – wind fetch
d – wind duration
Ucur – water currents
Ts – sea surface temperature
S – salinity
Ck – concentration, type (k) of surface active materials
6 Dec, 2011
Whitecaps and sea spray, Anguelova et al., NRL
5
Whitecaps signature
High
Reflectivity
Vis
6 Dec, 2011
Reflectivity
Emissivity
High
Emissivity
IR
Whitecaps and sea spray, Anguelova et al., NRL
mW
6
Remote sensing of sea foam
Microwave region
Advantages
e = (1 - W ) er + W e f
TB = e Ts
Transparent (almost) atmosphere
“...4% problem ...at 5 GHz,..., 90% problem at IR” (Swift, 1990)
Tractable atmospheric correction
Clouds penetration
Drawback
Low resolution
Smoother geophysical variability
Trade-off: global coverage
More data
Various conditions
6 Dec, 2011
Whitecaps and sea spray, Anguelova et al., NRL
7
Rough sea surface model
2-scale
Wave spectrum
e = (1 - W ) er + W e f
Anguelova and Webster, 2006
Anguelova et al., 2006
Durden/Vesecky/Yueh
Tuned for roughness only
Using WindSat code (v. 1.9.6)
© P.R.Hemington
z=0
Foam emissivity model
RT model
Layer with vertically non-uniform
properties
Distribution of thicknesses
Air, ε0=1
Foam, ε (z)
Courtesy of Prof. Cilliers
6 Dec, 2011
www.pbase.com/petehem/
Models
Whitecaps and sea spray, Anguelova et al., NRL
Water, ε
z = -d
8
Data
Independent sources
TB from WindSat
V, L from SSM/I or TMI
U10 and from QuikSCAT or GDAS
Ts from GDAS
S = 34 psu
Trade-off:
Sampling issues
Use long-term data
Sample count
6 Dec, 2011
Whitecaps and sea spray, Anguelova et al., NRL
9
Estimates of W
Improvements over the feasibility study (Anguelova and Webster, 2006):
More physical models
Independence of the variables
6 Dec, 2011
Whitecaps and sea spray, Anguelova et al., NRL
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Compare to photographic data
6 Dec, 2011
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Further development
Models
Higher resolution
Improved wave spectrum in 2-scale model
Comparisons/Validation
More points for direct comparisons
Indirect comparisons in terms of other variables
CO2 fluxes from ship cruises
o and COARE CO2 parameterization
AOD from AERONET
o and AOD from microphysical aerosol model
Uncertainty characterization
Currently uncertainty minimization
Evaluate the remaining using global geophysical model
6 Dec, 2011
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Whitecaps data base
All available orbits for
Resolution 50×70 km2
Time period
Entire 2006
Months of 2003, 2007 and 2008
Gridded data
With 0.5 x 0.5 grid box
Any other N x N possible
Time periods:
Daily
Monthly
Weekly (7 days)
3-days
6 Dec, 2011
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Geographic characteristics of W
March, 2007
0.5 x 0.5
Wind speed formula
W U103
Satellite, 10.7 GHz, H pol.
6 Dec, 2011
Whitecaps and sea spray, Anguelova et al., NRL
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Geographic characteristics of W
March, 2007
0.5 x 0.5
Wind speed formula
Satellite, 18.7 GHz, H pol.
6 Dec, 2011
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Develop parameterization(s)
W (U )
W (U , T , X , d ,U cur , Ts , S , C)
Relative importance of the variables
Correlation analysis
Wind
Fetch
SST
Stability
Wave height
Wave period
6 Dec, 2011
Whitecaps and sea spray, Anguelova et al., NRL
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New sea spray source function
dF (r , a, b,... )
= f(U ) f( r )
dr
Scaling factor Size distribution
Magnitude
Shape
Include wave-field characteristics and one
more factor W (U, H )
s
W (U , H s , Ts )
Improve/choose size distribution
Include organics
6 Dec, 2011
Whitecaps and sea spray, Anguelova et al., NRL
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Sea-salt flux
Annual sea-salt flux (1998)
Haywood et al., Science, 1999
Anguelova and Webster, 2006
2105
Solar irradiance at TOA
(W/m2)
:
4105
6105
8105
Number flux, dF (s-1 m-2 )
GCM – ERBE
NO aerosols;
Max difference over the
oceans.
6 Dec, 2011
Whitecaps and sea spray, Anguelova et al., NRL
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Sea foam definition
Oceanographic definition
Passive remote sensing
Whitecaps on the surface
Radiometers detect only the
Bubble plumes below
surface foam layers
Skin depth
At microwave frequencies
a few mm to a few cm
6 Dec, 2011
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Photographic measurements
High uncertainty: up to 30% or more
Intensity threshold
A and B stages under oblique angle
Stramska and Petelski, 2003
Patchy coverage
Open ocean
Southern ocean!
6 Dec, 2011
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Improvements and restrictions
(de Leeuw et al., 2011)
W (U10 )
W (U10 , T )
Whitecap fraction, W (%)
W (U10 , Ts )
6 Dec, 2011
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Modeling whitecap fraction
6 Dec, 2011
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