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This isn't really directly relevant for the form of weather modification - cloud seeding - discussed here, though. Generally speaking, cloud seeding doesn't fo

This isn't really directly relevant for the form of weather modification - cloud seeding - discussed here, though. Generally speaking, cloud seeding doesn't focus on state changes; you're not trying to materialize a precipitation cloud from clear air. It's straightforward enough to understand if a flow will lead to cloud formation. Generally speaking, it's also pretty straightforward with modern numerical weather prediction or large eddy simulations to predict whether those clouds that form will produce precipitation. The problem here is the counter-factual in the real-world. If you seed a cloud with an ice-nucleating substance like silver iodide, how will that change the balance of microphysical processes that lead to precipitation production? It's really, really hard to directly measure these, and it's not obvious that you can observe "the next cloud over" (e.g. in a cloud street or a convective field) as a null case. Furthermore, "observing" that cloud might involve flying an aircraft with cloud probes through it (it's not always the case that a terrestrial X-band or aircraft-mounted radar will provide all the information you need to close the microphysical budget), and of course the aircraft itself can perturb the cloud. This has really doesn't have anything to do with chaos or sensitivity to initial conditions. It's really just an issue of in the real world, we don't have a clean way to simultaneously measure the null hypothesis (what happens inside the cloud you don't perturb).

photochemsyn 4y ago
> "Since the early cloud-seeding experiments reported by Kraus and Squires (1947), wherein it was hypothesized that the observed “explosive growth” of cumuli was the result of artificially induced glaciation of the cloud, there has been intensive interest and research in the relationships between evolution of the ice phase and the dynamics of cumuli." As I understand it the idea is that a small amount of AGI or can cause nucleation which might trigger rainfall: > "Thus, the latent heat liberated during the freezing of supercooled droplets and the vapor deposition growth of ice particles can augment the diminishing cloud buoyancy production during condensation growth of cloud droplets. In some cases, the additional buoyancy may be sufficient to allow a cloud to penetrate weak stable layers or to survive the entrainment of relatively dry environmental air." The idea in cloud seeding is to hit a cloud 'on the verge of rain and push it over the boundary, but it doesn't seem straightforward at all to determine if a given cloud on that boundary will produce rain or not, as in a '50% chance of rain' forecast. It does indeed seem to be one of those chaotic boundary condition issues: > "This demonstrates that there exists a very intimate, nonlinear coupling between buoyancy production by glaciation of a cloud and the evolution of the microstructure of the cloud, and the evolving cloud motion field." https://www.sciencedirect.com/topics/earth-and-planetary-sciences/cloud-seeding https://www.sciencedirect.com/topics/earth-and-planetary-sci...
- counters 4y ago
  Thanks for sharing your reference. This is hysteresis, not "sensitivity to initial conditions" - a system is evolving on a particular semi-stable trajectory, and then gets nudged to a new one with a different equilibrium or evolution.

photochemsyn 4y ago

> "Since the early cloud-seeding experiments reported by Kraus and Squires (1947), wherein it was hypothesized that the observed “explosive growth” of cumuli was the result of artificially induced glaciation of the cloud, there has been intensive interest and research in the relationships between evolution of the ice phase and the dynamics of cumuli." As I understand it the idea is that a small amount of AGI or can cause nucleation which might trigger rainfall: > "Thus, the latent heat liberated during the freezing of supercooled droplets and the vapor deposition growth of ice particles can augment the diminishing cloud buoyancy production during condensation growth of cloud droplets. In some cases, the additional buoyancy may be sufficient to allow a cloud to penetrate weak stable layers or to survive the entrainment of relatively dry environmental air." The idea in cloud seeding is to hit a cloud 'on the verge of rain and push it over the boundary, but it doesn't seem straightforward at all to determine if a given cloud on that boundary will produce rain or not, as in a '50% chance of rain' forecast. It does indeed seem to be one of those chaotic boundary condition issues: > "This demonstrates that there exists a very intimate, nonlinear coupling between buoyancy production by glaciation of a cloud and the evolution of the microstructure of the cloud, and the evolving cloud motion field." https://www.sciencedirect.com/topics/earth-and-planetary-sciences/cloud-seeding https://www.sciencedirect.com/topics/earth-and-planetary-sci...

counters 4y ago
Thanks for sharing your reference. This is hysteresis, not "sensitivity to initial conditions" - a system is evolving on a particular semi-stable trajectory, and then gets nudged to a new one with a different equilibrium or evolution.