OCR Text |
Show aerovan e , it would be possible to c alculate a transport time for their 12 lllil trip from th e r e l e ase sit e to th e location of the counter. The forecast plullli arrival time s are shown. These have numbers corresponding to the seedin period from which they originated. They can be related in each case to a/ inc rease in nuclei concentration. No efforts have been made to rationalize the differ e nces in conc e ntration of th e diffe rent pulses. In Table 12 ar e found the transport times for each of the seven pulses, botn calculate d from the wind sp e ed and measured from th e plot of nuclei concen. traticn v ersus time. Relatively large differenc e s are s een between times o! individual pulses; however, the ave rage time of trav el for the seven pulses agre e s closely with th e ave rage of th e calculat e d times. An initial insp e ction of th e first se e ding p e riod would indicate the winds app to b e from th e wron g direction, but the ori g inal data from the Emerald aero, v an e sho ·vvs that a wind shift from 190 to 310 d e grees occurred just after OH MST. Thus, the indicated wind directions are somewhat misleading. Case 2, Figur e 7 4. Al though the winds above ridge leve 1 were a bit more rn therl y on this day th a n on 7 December 1966, the Emerald wind was the sam1, In this case, the concentration of ice nuclei at Rabbit Ears remained near backg round . Durin g this p.e riod a trac e r experiment was accomplished in conjunction with the r e gular seeding plan. Lithium stearate powder (inert a, both a condensation nucleus and as an ice nucleus) was emitted alongside th1 sil ve r iodide and was d ct c ct (; u at Rabbit Ears b y an aerosol flame photomel1 in con c entration s two ord e r s of m ag nitud e above background. The significM of thes e det ec t e d diff e r e nc e s between tracer and seeding material is uncert' as th e trace r \Vas ~mittcd only once under the conditions of this case. (Thal vv a s th e onl y time th e flame photomet e r was available.) However, there ha b e en oth e r inst a nces of wind dire c tion favorabl e for detection when only bad ground i ce nu c l e us conc e ntrations have be e n observed. I ne otl Ro nu C, M at Two ideas ar e advanc e d at this point which mi g ht help to explain the presenc of th e trac e r and absenc e of ic e nu c lei. One ls that nearly all of the silver iodid e particl e s were effe c tive as ice nuclei and resulted in snow . crystals \i, which, with any appr e ciabl e fall velocity, would not have entered the counter tr The tra ce r particles are not effective as ice nuclei and would not be so affec ir The s e cond idea is based on pr e fer e ntial scave n ging of the particles by the w snow which was fallin g at that tim e . The m e an mass diameters of the silve'. iodide and lithium s t e arat e particle s ar e about O. 55-. 10 u and 2-5µ, respec B e c ause of these diffe r e nt si zes o n e mi ght ex pect differ ~nt scavenging efficl e n c i e s, both from a m ec hani c al and diffusive v i e wpoint. Case 3, F i gu re 7 5. Here an inve rsion was definitely present, as indicated~ the m o de rat e wes t erli es at 11, 000 f ee t MSL and th e li crht southerlies (chan to n or t her l y) at Emeral d . Durin g th e E mer ald wind direction switch at 09~1 124 |