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Posted at 1:30 PM ET, 02/20/2009

Artificial or Not, China Has Snow and D.C. Doesn't

By Steve Tracton

* Our Full Forecast | Weather Channel Founder Talks Climate 'Scam' *

So you want snow in D.C.? If so, perhaps we need to follow the example of China.

As reported here and here, Chinese officials claim that the first snowfall of the season this week in Beijing was produced artificially by cloud seeding. As part of an effort to alleviate a persistent drought in the region, sticks of silver iodide are being launched by rockets into clouds to serve as the catalyst for initiating precipitation. These same officials claim that the only other precipitation this winter -- rain last week -- was also the result of cloud seeding.

Haven't we heard this before? Yep...

Keep reading for more on China's ongoing weather modification efforts...

As I reported last summer, China's weather modification program -- arguably the largest in the world -- claimed success in preventing rain from ruining the opening ceremony of the Olympics by making clouds "rain out" before reaching the Olympic stadium.

Unfortunately for those around here grasping at straws for snow, China has never provided verifiable documentation counter to the prevailing view, as stated in a National Academies report, that "There is still no convincing scientific proof of the efficacy of intentional weather modification efforts."

In other words, the snow at Beijing might very well have occurred naturally. And we don't know to what extent seeding has failed to produce the desired outcome on other occasions.

Side Note: The MSNBC report notes that "Beijing's drivers are still getting used to maneuvering in the snow" -- sound familiar?

By Steve Tracton  | February 20, 2009; 1:30 PM ET
Categories:  International Weather, Tracton  
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Next: PM Update: Winds Weaken, But Cold Overnight


Dr. Tracton,
It is true that the Chinese have provided little scientific proof of the efficacy of their weather modification successes through the open literature. I am particularly skeptical of rocket-borne seeding material delivery.

However, the National Academies report gives a misleading blanket statement that ALL weather modification activities show no proof. One of the authors of the report, Dr. Roelof Bruintjes, would likely agree. He has been involved with projects showing clear promise for hygroscopic (salt) seeding of warm convective clouds. And there has been statistical evidence that winter orographic seeding has produced seasonal increases in precipitation. This statement is supported by the American Meteorological Society and the WMO in their policy statements - the AMS even gives an approximate figure for the increase of 10%.

That is not to say that cloud seeding is in need of more research. There was a six-state weather modification research program sponsored by the U.S. Bureau of Reclamation from 2002-2006. This cooperative applied research showed some promising findings. We need to follow up on these findings through Federal involvement as before. Two bills for such a weather modification research program, sponsored by Kay Bailey Hutchinson in the Senate, and Mark Udall in the House, have languished without funding for several years now.

We need to explore all means of providing water to an increasingly parched world. Cloud seeding has been around for over 50 years, and like the National Academies report asserts, has yet to take advantage of the latest developments in atmospheric science to bring it to fruition.

Posted by: pulsepair | February 21, 2009 2:48 AM | Report abuse

The radar pulse pair method is an important tool in investigating the physical properties of clouds, including increased understanding the mechanisms responsible for the formation of precipitation. However, cloud physics is not the real problem of successful weather modification. Any attempt to enhance rain or snow in a specific cloud system or region must face the reality that it is a zero sum game - literally robbing Peter to Pay Paul. Cloud seeding might increase the precipitation in one area, but that likely means somewhere else precipitation will be reduced. Seeding does not increase the amount of atmospheric water vapor available for formation of rain or snow, only the timing and region precipitation is produced. Without a mechanism to actually increase the available water vapor ("precipitable water"), enhanced precipitation in one area can only be at the expense of some other region.

The key deterrent to weather modification efforts is not really lack of understanding precipitation physics , but rather the legal implications pitting the winners versus the losers. In a larger context where winners and losers might be countries, International law prohibits weather modification.

Posted by: SteveT-CapitalWeatherGang | February 21, 2009 12:23 PM | Report abuse

I agree that legal and social implications frequently arise with the common perception of "Robbing Peter to Pay Paul," as you have described. And this idea needs much more research for complicated summer convective clouds. As for winter orographic storms, however, it is a different scenario. In this case, the idea that precipitation increases in one area cause decreases elsewhere is a misconception. The amount of atmospheric moisture passing over a mountain barrier that is converted to precipitation is usually 10% or less (natural precipitation efficiency). If this natural precipitation is increased 10% by cloud seeding, the seeding depletes only 1% of the original atmospheric moisture supply, the remainder of which (99%) is available for precipitation downwind. More importantly, winter cloud seeding is done on clouds on the upwind side of mountain ranges. These clouds usually dissipate on the downwind or lee side of the range, because of subsidence and adiabatic warming (the “rain shadow”). As you know, this is the reason that lee side areas like the Colorado Front Range and Nevada are much drier than on the upwind side of the mountains. So the atmospheric moisture supply on the lee side of the mountain range will not likely precipitate anyway. Finally, precipitation data from a number of long-term cloud seeding projects have been examined in detail for evidence of "extra-area" effects. These examinations do not show that seeding clouds with silver iodide causes a decrease in downwind precipitation; in fact, most studies indicate an INCREASE as far as 100 miles downwind of the target area. I can share the numerous scientific references for this information if you'd like.

Posted by: pulsepair | February 23, 2009 2:31 AM | Report abuse

pulsepair, I defer to your expertise on this subject.

I gather from what you say that seeding on the upwind side, when little if any precip is likely on the lee side, is a special circumstance where seeding can be effective - essentially increasing the efficiency of precipitation formation mechanisms.

But, cannot the distribution of precip on the downward side be affected as a function of where the seeding is done? I suspect the answer is probably not, as long as the precip is stratiform. If there was convection embedded,it would probably make more of a difference. This would be especially true if seeding was attempted on the downwind side of the Sierra where precip is much more convective in nature - even in winter.

Thanks for your welcome comments - Steve

Posted by: SteveT-CapitalWeatherGang | February 23, 2009 3:52 PM | Report abuse

You're most welcome. The studies I was referring to have to do with so-called "extra-area" seeding effects, or precip (or seeding material) influences beyond (usually downwind) of intended target areas. One of the proposed physical mechanisms hypothesized for these increases was the "seeder-feeder" mechanism, whereby silver iodide still active would fall into a lee side stratiform cloud (or be entrained by embedded convection there) and take advantage of supercooled liquid water (SLW) to augment precipitation.

So you are correct. By seeding on the crest, or even on its lee side, one would expect by the same logic that one could increase the precip on the lee side even more, provided the right cloud conditions there.

The bottom line is that targeting of seeding material into the right cloud conditions (temp, SLW, lack of natural ice nuclei), then having the resultant precipitation fall into the target area, is one of the most challenging obstacles to effective seeding.

PS I used to administer a 6 state seeding research program in the Dept. of the Interior.


Posted by: pulsepair | February 24, 2009 11:28 AM | Report abuse

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