What the Southeast <cite>Really</cite> Needs is a Hurricane

Can cloud seeding help the southeastern United States from going Mad Max in the next 90 days? Mike MacCracken, chief scientist over at the Climate Institute, was the next to answer my query, and he doesn't think it'll help. Wrote Mike,

While I suspect there is moisture in the air, getting a rain system going requires not only nuclei on which drops can form (and given the air pollution in that region, I suspect that cloud condensation nuclei are not in short supply), but an instability in the air mass that can help keep it going (like cool air—a cold front-- coming in underneath because the air is denser and helping to start forcing upward movement of the moist air, or cooling aloft that makes the vertical column unstable and so the warm air starts rising). Right now, I think the problem at these latitudes is that air masses are rising toward the equator and coming down over Atlanta and other subtropical areas, and so downward moving air is stable and warms, and may even be quite dry. Cloud seeding would not work in such situations, in my view.

What they really need is a near stationary tropical cyclone moving over them that will suck in moist air and cause it to rise, wringing out the moisture as heavy rains. It is too bad that tropical Storm Noel is out to sea, pushed out by a cool front, etc. That is what they need.

That response rang a bell -- I half-remembered reading something about
MIT climate scientist Kerry Emanuel's proposal to deflect or adjust the course of hurricanes. Would it be possible, I asked Mike, to steer a storm to a desired area or otherwise attract it to the southeast? Mike responded,

There were some experiments done in the 1950s and maybe early 1960s to see if one could alter a hurricane (e.g., reduce its intensity, etc.).
Experiments had to be done way out at sea in case made things worse so would not be endangering land and then ended up stopping effort as hurricanes were not well enough understood to know if what was changing was a normal fluctuation or an induced change. We now have pretty detailed hurricane models that could try experiments on, though models are much better at track than at intensity—which changes in ways not yet understood. What Kerry Emanuel wanted to see if he could explore was whether one might cause a small change in the weather somewhere and then have confidence that this would develop into or alter a weather front to be able to push a hurricane away from some major city—all quite theoretical at moment, and not at all clear it would work. Also, intent was mainly to use weather fronts to protect US mainland—not at all clear it would even be conceivable to try to change a front to attract a storm on land, as would like to do for present tropical cyclone.

The problem we seem to have now might be resulting from how Pacific
Ocean temperatures are aligned, deflecting the jet stream in such a way that the air getting to the Atlanta region is dry continental air—likely created when Pacific moisture was forced out as air got lofted over the Rockies, Sierras, or Cascades, etc. So, really hard to get changes—and anomalies tend to persist for months until other forcings (like Sun movement as part of seasonal cycle) cause things to switch.

I left a message with Emanuel, so hopefully we'll find out what he thinks. Who knows -- maybe he's figured out exactly how to make a butterfly flap its wings so that rain falls over Alabama.

Image: [Climate Prediction Center, NOAA/NWS](http://www.drought.unl.edu/dm/monitor.html)

See Also:

• Feds Propose Truce in Southeast US Water Wars
• A Chance of Snow
• Global Climate Engineering: Who Controls the Thermostat?
• Cloud Seeding Won't Bring Rain to the Southeast, Says Climatologist