 |
|
|
|
|
| 3/9/2009 6:00:00 AM | Email this article • Print this article |
+ click to enlarge
|
Photo Courtesy of Larry Hjermstad
A cloud seeding generator is fired up by Larry Hjermstad’s son, Mike left, on Robert and Gayle Knoor’s property north of Silverthorne, Colo. Silver iodide molecules, which are invisible to the naked eye, are propelled into the cloud system to eventually help increase snow conditions farther downwind. |
| | World hopes to squeeze more fresh water from clouds | By Kristen Plank
Journal Staff Writer
Weather modification programs are taking the world by storm.
Eleven U.S. states and 37 countries worldwide participate in programs from precipitation enhancement to hail suppression.
Cloud seeding, or the process of increasing precipitation in a cloud system by external means, started gaining interest in the late 1940s, said Dan Breed, a project scientist at the National Center for Atmospheric Research.
"First there was the discovery that putting dry ice into super-cooled clouds can create ice crystals that eventually precipitate out," Breed said. "What followed quickly was when (scientists) found that silver iodide acted as an ice nuclei, which started a flood of interest in cloud seeding as well as some wild speculations as how effective that might be."
Silver iodide is a compound that closely resembles an ice crystal and, when ejected into the atmosphere from an ice nuclei generator, is known to increase precipitation in certain cloud systems.
The U.S. Bureau of Reclamation took over many cloud seeding projects in the late 1970s, but funding for cloud physics - and consequently cloud seeding - dropped off soon afterwards, Breed said. Now, NCAR is involved in feasibility studies all over the world to increase knowledge of cloud seeding effectiveness.
"The whole premise behind cloud seeding is to squeeze out any additional precipitation from a cloud system," Breed explained. "Clouds and storms are inefficient producers - a lot more water vapor goes into a cloud than comes out, so a little push can give it a fairly significant effect."
The need for additional precipitation is not just a concern for semi-arid states in the West but also for countries all over the world.
"With an increased population as well as climate change, there is a lot more pressure for fresh water all over the world," he said. "The No. 1 reason that entities or governments look to cloud seeding as a possibility is to enhance their fresh water supplies."
While increased pollution in the atmosphere might negatively affect how a cloud system generates precipitation, the larger picture is still unknown, Breed said.
"By and large I would say that pollution tends to suppress precipitation, but the magnitude of anthropogenic (human) influence on climate is still such a big unknown."
Reach Kristen Plank at kristenp@cortezjournal.com.
|
|
Cloud seeder harvests rain for water conservancy district
Kristen Plank
Journal Staff Writer
Keeping clouds heavy with precipitation is Larry Hjermstad's forte.
The Durango-based weather wizard has been conducting his magic on Colorado clouds for more than 30 years by "seeding" the sky with a material known as silver iodide. This compound is used to augment the amount of precipitation coming from a cloud system, creating additional snowfall over certain areas.
Hjermstad, founder of Western Weather Consultants LLC, seeds locally for approximately 10 different entities that support the cloud seeding program, from the town of Telluride to the Dolores Water Conservancy District.
The DWCD invests in two of Hjermstad's cloud seeding programs in hopes to increase inflow into McPhee Reservoir. Mike Preston, manager for the DWCD, said the water district has played a part in the program since 2000, and paid approximately $17,000 for the 2008-2009 winter program.
"Ski areas are investing in the program for the snow to ski on, but our interest is pure and simple," Preston said. "If we can increase the inflows into the McPhee Reservoir by some percentage, then everyone benefits."
Hjermstad recounted an independent study done by Bernard Silverman, prior chief scientist with the U.S. Bureau of Reclamation, that showed the effects of a 33-year cloud seeding program on Vail's surrounding streams. The study, lasting from 1977 to 2005, showed an eight to 30 percent increase in stream flows.
"(Silverman) wasn't looking at snow as being of value, but rather water as being of value," Hjermstad said. "The study verified that precipitation increases are reflected in stream flow increases. To me, this is the missing 'ground link' for what we are trying to do with precipitation."
Hjermstad releases study results to water managers like the DWCD every year before contract renewals. Studies such as these are important for Preston and other board members so they know the money they spend on seeding is well spent.
"We are very pro-research on (cloud seeding) verification," Preston said. "Under ideal circumstances, we would like to fill the reservoir brimful, and if cloud seeding means filling to brimful or not filling it, then we want to fill it."
Any additional precipitation that can increase inflows into McPhee will eventually aid in decreasing shortages during drought years, he said.
Cloud seeding, or weather modification practices, is a popular process throughout the world. Locally, a total of 34 "ice nuclei" generators are spread across the San Juan Mountains, working from November through the end of March. Hjermstad will have operators turn on generators for roughly 24 storms during a three-month period.
Not every winter season storm that rolls into the area is seeded, Hjermstad said. Meteorologic conditions must be met first.
"When we see a weather system coming in, we ask what the meteorologic conditions are and if there is room for additional help to make those cloud systems precipitate more," Hjermstad said. "Once we determine the 'target area,' we will place a network of ice nuclei generators upwind so that we can handle various wind directions, and a plume of nuclei will travel downwind into that cloud system area."
Well over a trillion seemingly invisible silver iodide nuclei will work their way into the bottom portion of a cloud system, where they will attract moisture, produce snowflakes and fall to earth. The compound works so well at producing additional snowfall because of its nearly identical characteristics to an ice crystal. It's as safe as one, too, Hjermstad said.
"One reason silver iodide was chosen was because, as a molecule, it is extremely tightly held together once the two elements combine," he said. "Nothing in nature breaks it apart."
This includes the sun, the photosynthetic process in plants, or anything from the digestive systems of humans, animals or aquatic wildlife. Hjermstad said that cloud seeding programs also do not take away from any precipitation that may have been dispersed into towns downwind.
"If there is an effect, it's very small and it's a positive effect," Hjermstad clarified. "What happens downwind is a slight increase from what they normally would have had, though not the same effect over the area you are seeding."
This is due to the energy created during the "pluming" process; leftover energy then travels to its original destination. Depending on wind flow, seeding takes effect approximately 15 to 20 miles downwind, or 30 to 40 minutes after nuclei have been released.
Hjermstad, whose company has five operations throughout Colorado, hopes to extend the range of the cloud seeding program to encompass other municipalities and entities.
"We have a fairly extensive list of people involved in our program at various financial and interest levels, and we are trying to invite other municipalities as well," he said. "There's still room to do more, and having more people involved will make it a more effective and longer producing program."
Reach Kristen Plank at kristenp@cortezjournal.com.
|
Article Comment Submission Form
|
|
|
|
|
