Conclusion -75- 



Observed results of the seeding of stratus clouds indicate that holes 

 can be cleared in them by this method, which is bound to be of value in 

 aircraft operations. 



Modifying Supercooled Ground Fogs . Supercooled ground fogs formed 

 by advection or radiation may be modified and even dispersed if care is 

 exercised to prevent overseeding. Too high a concentration of ice nuclei 

 introduced into such fogs might actually make the fogs worse. 



The prevention of the formation of ice fog is another possibility 

 from the proper manipulation of seeding techniques. By introducing an 

 optimum number of sublimation nuclei into the air in regions where such 

 fogs are troublesome, it may be possible to continuously remove from the 

 air the moisture responsible for the formation of this interesting but of- 

 ten troublesome type of ground fog. 



The ice crystals generated in the vortices of airplane propellers 

 plus the moisture added to the air by the combustion exhaust of the plane 

 are the causes which generally lead to the formation of ice fogs at air- 

 ports. Whether the removal of supersaturation with respect to ice by 

 seeding methods will be of sufficient magnitude to prevent the ice-fogging 

 effects produced by plane operations can be determined most conclusively 

 by actual experiment. 



Protection of Aircraft. There is no question about being able to 

 modify icing clouds in the vicinities of airports and along heavily traveled 

 air lanes. The problem rather, is whether it may have a practical appli- 

 cation. Low clouds which restrict visibility for landing approaches around 

 airports, thick clouds in which planes must cruise as they wait for per- 

 mission to land, and thick clouds which might deposit a serious icing load 

 on the plane as it tries to climb up through them--these comprise hazards 

 to safe plane operations. And when such clouds are supercooled, they may 

 be profoundly modified. 



The simplest means for carrying out such cloud modification would 

 be to employ a plane well equipped for flying under serious icing condi- 

 tions for patrolling the air lanes. The plane would report weather and 

 cloud conditions and, whenever serious supercooled clouds occurred, 

 would carry out seeding operations. 



In flying through a supercooled cloud, the airplane itself may pro- 

 duce a fairly effective modification. The vortices which form at the 

 trailing edges of the wings and particularly from the propeller tips form 

 large numbers of ice crystals. 



