Solar radiation management by use of air lubrication method

Suginori Iwasaki and Nanami DoiNational Defense Academy, Japan.

Figure from Lenton and Vaughan (2009, ACP)

All geoengineering methods do not make any profit.

Introduction 1

2

3

The ship wake photo of ALM experiment (from Dr. Hinatsu, NMRI).

Diagram of the ALM (Mizokami et al. 2011).

bow

stern

air supply opening

bubble flow

Ship wake

Bubbles of ALM + Ship wake

The reflectance and area of ALM bubbles are greater than those of ship wake.

Fuel efficiency = +8-12% (Mizokami et al., 2011)

Introduction 2: Air Lubrication Method (ALM)

4

Simulate the bi-directional reflection distribution function of ALM by the ray-tracing method.

Estimate radiative forcing of ALM bubbles.

Gatebe et al. (2011) showed the radiation forcing of normal ship wakes was -1.4×10-4 W/m2, ~10-4 times smaller than that of CO2.

Previous study

This study

Introduction: 3

5

Method 1: Ray-tracing method

Decide scattering / absorption by random numbers Scattering: Mie scattering

Absorption: Lambert-beer law

Stop below draft

Count

ininλ

outoutλoutoutininλ ,

,,,,

F

IBRDF

Count(θ out,φout)

(θ out,φout)

(θ in,φin)

6

Method 2: Bubble distribution

homogeneous & log-normal distribution

Bubbles size distribution of the experiment of ALM, Nagamatsu et al. (2002)

draft: 5m

Mode radius: 308µmStandard dev.: 1.67Number density: 1.28×105/m3

Total vol. of bubbles: 2mm/m2

τ ~ 20s (Garrett, 1967)r = 50% (Whitlock, 1982)

7

Results: Bi-directional Reflective Distribution Function (BRDF)

 Obs. of normal wakeGatebe et al. (2011)

Simulation 1Test vessel

308μm, 2mm/m2

Simulation 2Imaginary vessel 30μm, 5mm/m2

Averaged BRDF 0.032 0.14 0.37

ALM test vessel308 µm and 2mm/m2

bubbles

ALM imaginary vessel30 µm and 5mm/m2

bubbles

Time [hours]Time [min]

8

Radiative forcing

Radiative forcing = 　 solar flux on sea surface (W/m2)　　　 (W/m2) 　　　 × 　 number of ships　　　　　　　　　　　 × 　 wake area / Earth area 　　　　　　　　　　　 × 　 wake albedo (Liang et al., 2005)

We simply estimate the radiative forcing by ALM bubbles,

Gatebe et al. (2011, GRL)

=BRDF of 1 vesselNormal albedo

BRDF of 1 ALM vesselALM albedo

Gatebe et al. (2011)

If all have ALM

9

Results: Normal wakes vs. ALM wakes

1. Wake area, lifetime of foam, is needed to research!

2. Smaller ALM bubbles would have a potential for geoengineering.

# GHG emission of all ships is 2.7% of the global total (Second IMO GHG Study 2009).

  Normal wakeGatebe et al.(2011)

ALM wakeTest vessel

308µm, 2mm/m3

ALM wakeImaginary vessel30µm, 5mm/m3

Av. albedo 0.018 0.079 0.21

Wake area (km2) 　　　 2.17

0.02 4.5

Radiative forcing (W/m2) −1.4×10-4 −5.7×10-6 −3.4×10-3

×100

×25

coast294m

ocean105m

ocean105m