Design of Marine Cloud Brightening Operations

The design of wind powered vessels for delivery of marine cloud brightening is reasonably advanced. Salter et al. [1] offered initial designs of such vessels, considered mechanisms for suitable salt water spraying, and explored promising locations for cloud brightening. We are unaware of publications investigating efficient ways of routing these vessels. This paper offers a consideration of such routing.

A model for optimal routing comprises two parts. The first is the performance of the vessels. We assume the motive power is provided by Flettner rotors. Existing models use a single rotor; we are investigating a dual rotor configuration. Early results suggest considerable interaction between the rotors, with one rotor producing up to 30% less lift than the other. This has an apparent impact on vessel performance.

The second part seeks efficient routes for the spray vessels. Two phases of operation require analysis. The first is the translocation of the vessels to a suitable location. Vessels may journey between hemispheres in order to operate in the sunnier environment - for this one might try to minimise journey time. This is a classical problem solved by dynamic programming. The search space is discretised, with wind, currents and vessel power combined to estimate transit time between adjacent nodes. For the wind, historical reanalysis data can be used. Interesting points arise regarding the probability distribution of the total transit times.

Once the vessel is located at a suitable spraying position, routing will be selected to optimise target cooling. Again the search space is discretized, but here the optimisation method is not obvious. Dynamic programming is no longer efficient because after each step, all adjacent nodes remain possible candidates for the next. The family of possible routes grows exponentially. Early experiments produced reasonable routing but the optimum is worth investigation.