PART V — SEVERE STORMS 



Development of still more sophis- 

 ticated prediction models depends on 

 a better means of observing the in- 

 teractions between large and small 

 scales of motion. The major emphasis 

 of the Global Atmospheric Research 

 Program's first tropical experiment, 

 scheduled for the Atlantic Ocean in 

 1974, will be to describe and under- 

 stand cloud clusters. The results of 

 this investigation should provide 

 valuable guidance in modeling the 

 interaction between meso- and syn- 

 optic-scale motions. For the imme- 

 diate future, however, the emphasis 

 will probably have to remain on 

 development of numerical methods 

 that will minimize errors in predict- 

 ing tropical disturbances and storms. 

 Unless vast resources are devoted to 

 the problem, sophisticated prediction 

 models are not apt to become avail- 

 able in less than five to eight years, 

 if then. 



The median error in predicting the 

 landfall of hurricanes along a U.S. 

 coastline continues to decrease slowly, 

 although it varies from year to year. 

 This progress is due not so much to 

 advances in modeling hurricanes 

 numerically as it is to the availability 

 of better facilities to track and ob- 

 serve disturbances at each stage of 

 development and of modern tech- 

 nology that provides rapid processing 

 of data from the storm area and 

 environment. These facilities permit 

 us to apply diagnostic tools of rea- 

 soning in an objective fashion, though 

 we have only scratched the surface 

 in the development of such tools. 

 Apart from any progress that might 

 be made in modeling the behavior of 

 hurricanes, there is good reason to 

 estimate that the median error for 

 predicting hurricane movement near 

 our coastlines, now about 110 nauti- 

 cal miles for a 24-hour movement, 

 can be reduced by 30 to 40 percent. 

 This depends, however, on exploiting 

 information from the meteorological 

 satellite to obtain numbers — rather 

 than impressions — concerning the 

 physical character of the environment 

 in which the hurricane or its seedling 

 moves. 



Basic Understanding of the 

 Hurricane System 



While much has been learned 

 about the hurricane, its structure, 

 and the energetics that cause a seed- 

 ling disturbance to develop, there 

 remain notable gaps in the funda- 

 mental understanding of the hurri- 

 cane system. The first is the puzzle 

 of why so few hurricanes manage 

 to develop from the abundance of 

 seedlings that parade across the tropi- 

 cal scene. Secondly, the hurricane is 

 basically an unstable system varying 

 in intensity from day to day and 

 even from one six-hour period to the 

 next, but the reasons for these varia- 

 tions are not understood. The whole 

 concept of weather modification in 

 hurricanes may depend on a better 

 understanding of the natural instabil- 

 ities in this delicately balanced sys- 

 tem. 



Answers to these questions will 

 probably depend on a concerted pro- 

 gram of field experimentation and 

 numerical modeling. To pursue the 

 problem only through numerical 

 modeling is risky for the simple 

 reason that, in so complex a system, 

 the modeling problem becomes in- 

 tractable unless there are extensive 

 uses of approximations, parameteri- 

 zations, and other mathematical sim- 

 plifications which, while yielding in- 

 teresting results, may only crudely 

 simulate the real atmosphere. Ex- 

 perience has shown that the best 

 results come from a two-pronged 

 program which, in step-wise fashion, 

 produces a model for one facet of 

 a development and then verifies the 

 result of this simulation by field 

 exploration in the real atmosphere. 



Prospects for Reducing the 

 Hurricane Hazard 



Ideally, one would like to find some 

 means to prevent all hurricane seed- 

 lings from developing into severe 

 storms while retaining the useful 

 rainfall carried by these disturbances. 

 Although many suggestions have 



been made for cloud-seeding or other 

 cloud-modifying measures to curb 

 the formation of hurricanes, none has 

 comprised a physical hypothesis that 

 has considered both the cloud proc- 

 esses and the circulating properties 

 of the cloud environment. 



It appears more and more likely 

 that the formation of a hurricane is 

 something of an accident of nature, 

 at least with regard to the particular 

 cluster of clouds in which the event 

 occurs. In general, a storm center 

 tends to form somewhere in an en- 

 velope of rain clouds spread over 

 hundreds of miles. But there is still 

 no reliable means of predicting which 

 particular cluster nature will pick to 

 foster the growth of a storm center. 

 Therefore, even if one knew precisely 

 what modification techniques to ap- 

 ply to a cluster of clouds (no more 

 than 25 or 30 miles in diameter, for 

 example) — and one does not know 

 this yet — it would be impossible to 

 know where to send the aircraft to 

 conduct the seeding or take other 

 preventive actions. 



Cloud Seeding: Project STORM- 

 FURY — As for curbing the fury of 

 the hurricane, it must be conceded 

 that, at present, the only hope lies 

 in identifying, and hopefully treading 

 on, the "Achilles heel" of a delicately 

 balanced storm system — its ability 

 to release latent heat under certain 

 circumstances. That is precisely what 

 the Project STORMFURY hypothesis 

 seeks to accomplish. 



While scientists do not yet fully 

 agree on the benefits to be expected 

 from systematically seeding hurri- 

 canes or seeking in other ways to 

 upset the balance of forces in the 

 storm, those who have followed the 

 STORMFURY experiments cannot 

 help but be excited about the very 

 encouraging results obtained in 1969 

 from Hurricane Debbie. If the same 

 order of response from cloud seeding 

 is obtained in one or two additional 

 experiments, it will be possible to 

 demonstrate beyond a reasonable 



126 



