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A New Hail Suppression Project Using Aircraft

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A New Hail Suppression Project Using Aircraft "NON-REVIEWED" ,’-~RIL 2000 [(RAUSS ET A NEWHAIL SUPPRESSIONPROJECT USING AIRCRAFTSEEDING IN ARGENTINA by ¯ Terry W. Krauss* RoelofT. Bruintjes HugoMartinez WeatherModification Inc. National Centerfor Atmos- UniversidadNacional de Fargo, North Dakota pheric Research Cuyo - CONICET Boulder, Colorado Mendoza,Argentina INTRODUCTION OPERATIONALSEEDING PROGRAMDETAILS The Province of Mendozain western Argentina (32 S., 68 deg W.) is one of the most hail prone The current operational seeding period is from areas of the world. Lossesto agriculture dueto October15 th to April 1~t. Themain radar is cen- hail historically are >10%of total annualagricul- trally located at Cruz Negra(33.447 deg south, tural production. The region is knownas the 68.967 deg west) near Tunuyan.The project area "Landof Wine"and the principal crops are grapes covers the three agricultural oasesof Mendoza- plus a large variety of fruit andvegetables (e.g. SanMartin in the north, Tunuyanin the center, apples, cherries, peaches,apricots, plums,mel- and SanRafael in the south. A mapof Mendoza ons, garlic, tomatoes). Theprovince comprises province and the target oasesis shownin Fig- diverse territory of mountains,upland areas, and ure 1. The programconsists of 3 Piper Cheyenne plains. The western border of Mendozais occu- II seedingaircraft, 1 LearJet research-seederair- pied by the mainAndean cordillera, with a number craft, two C-band weather radars with TITAN of peaks above 6400m.Climatic conditions are processingand display software, two Vaisala ra- ¯semi-arid, andthe annualrainfall for the Capital diosondesystems, plus all the necessarystaff. City Mendozais 200 mm. TwoCheyenne II are stationed at SanRafael, the Hail suppression programsus- ing Russian rocket technology have been conductedin the re- gion since 1985with someinter- ruptions (Makitov 1999). A new airborne hail suppressionproj-. ect has nowbeen implemented ..... by Weather~.Modification ..Inc.....-; (WMI)of Fargo,i...North~Dakota;.... for the Ministry of Economy, Governmentof " Mendoza, gentina. A one-year program was conducted from Dec. 4th 1998 to April 15th, 1999 to. demonstratethe capabilities of airborne hail suppressiontech- niques and methodologies. In October1999, in responseto an international request for bids,. WMIwas awarded a 5 yr con- tract to continuethe operational" seeding programand implement a technologytransfer and re-. searchprogram. Figure. 1: Mapof MendozaProvince, Argentina showing the three areas of operations:, North (Mendozaand San Martin), Central (Tunuyan), and South *Correspondingauthor. (San Rafael). Email: [email protected] Me~o;taTake-Offand Lar~gs (4-~e¢-98 to 28-Mar.99- 206Ffghts) the hail growth process. Someof this complexity is reviewedin the paper of Foote (1985) that at- temptsto classify a broad spectrumof .storm types ,o....o ..... " i ._.!_J_ [ ..i_!.__.!... ’ . - ...... according to both dy- namical and microphysi- cal processesthought to ~ To ¯ - - L .~ ...... ~__..1...._..[: _2...... ~___-:.--.~-_~ _L be critical to hail produc- tion. Thegrowth to large hail is primarily hypothe- sized to occur along the edgesof the main storm updraft wherethe merg- ~meof Day(UTC) ing feederclouds interact with the main storm up- draft (WMO,1995). Figure 2: The frequency of occurrence and cumulative distributions of air- The cloud seeding hy- craft take-off and landing times for all flights as a function on time. Local pothesis in Mendozais .time is 3 hrs behind universal (UTC) time. Approximate summer sunset based on the concept of and sunrise times are indicated. "beneficial competition". Beneficial competition assumesa deficiency of other CheyenneII and the Lear Jet are stationed natural ice nuclei in the environmentand that the injection of silver iodide (Agl) will result in the at Mendoza. The Cruz Negra radar operates continuously. Radarimages are madeavailable productionof a significant number.of"artificial" ice nuclei. Thenatural andartificial ice crystals "com- on the VVWVVinternet at 15 min intervals. All of the project’s radar data, meteorologicaldata, air- pete" for the available super-cooledliquid cloud craft data, and reports are recorded onto CD- water within the storm. Hence,the hailstonesthat ROMfor the Ministry of the Economy.The audit- are formedwithin the seededcloud volumeswill ing of the operationalprogram is being conducted be smaller and produce less damageif they shouldsurvive the fall to the surface.If su~cient by the NationalUniversity of Cuyoin Mendoza. nuclei are introducedinto the newgrowth region of the storm, then the hailstones will be small CONCEPTUALHAIL MODEL enoughto melt completely before reaching the ground. Cloud seeding operations alter the mi- crophysics of thetreated clouds, assumingthat The cloud seeding is based on the conceptual the presentprecipitation processis inefficient due modelof Alberta hailstorms which evolved from the experimentsand studies of Chisholm(1970), to a deficiency of natural ice nuclei. Cloudseed- ing doesnot attemptto competedirectly with the Chisholmand Renick (1972), Bargeand Bergwall energyand dynamics of the storm. Anyalteration (1976), Kraussand Marwitz (1984), and English of the storm dynamicsoccurs as a consequence (1986). Direct observational evidencefrom the of the increasedice crystal concentrationand ini- instrumentedaircraft penetrationsof Coloradoand Alberta stormsin the 1970’sand early 1980’sindi- tiation of riming andprecipitation sizedice parti- cates that hail embryosgrow within the time cles earlier in the cloud’slifetime. Thesilver-iodide reagentsinitiate a condensation-freezingprocess evolving "main"updraft of single cell stormsand within the updrafts of developing"feeder clouds" and produce enhancedconcentrations of ice crystals that competefor the available, super- or cumulustowers that flank mature"multi-cell" and "super-cell" storms (see e.g. Foote, 1984; cooledliquid water in a storm andthereby reduce the growth of large damaginghail. The seeding Krauss and Marwitz, 1984). The computationof also initiates the precipitationprocess earlier in a hail growth trajectories within the context of cloud so that cloud hydrometeorsmay proceed measuredstorm wind fields provided a powerful newtool for integratingcertain parts of hail growth via an ice-phase(graupel) to rain mechanismin- stead of continuingto growto damaginghail. theories, andillustrated a striking complexityin "NON-REVIEWED" 75 APRm2000 CLOUDSEEDING METHODOLOGY" -6°C,-8°C, -10°C, and-12°C.The flares used in Mendozaproduce between1012 and 1013 ice nu- Stormcells (defined by radar) with maximumre- clei per gramof pyrotechnic between-6°C and - flectivity >35dBZ within the cloudlayer abovethe 10°C. The newgeneration ICE pyrotechnic pro- -5oC level, located within the project areas or duces>101~ ice nuclei per gramat -4 C. Ratesof within a 20 mintravel time "buffer zone"upwind of. ice crystal formationin the CSUisothermal cloud the project areas, are seedingcandidates if they chamberwere extremely fast (63%active within are deemedto be a potential hail threat. Radar one to two minutes, and 90%active within four meteorologists are responsible for makingthe minutes) and the apparentice formation mecha- "seed" decision anddirecting the cloud seeding nismwas identified as condensation-freezingnu- missions, incorporating the observationsof the cleation (Demott,1999). Significant ice formation pilots into their decisions.Patrol flights are often activity was measuredas warmas -4°C. Little launchedbefore clouds within the target area dependenceof yield on cloud liquid water content meetthe radar reflectivity seedingcriteria. These or clouddroplet distribution characteristicsis ex- patrol flights are meantto providea quicker re- pectedbased on the current tests. High yield and sponseto developingcells. In general,a patrol is fast acting agentsare importantfor hail suppres- launchedin the eventof visual reports of vigorous sion since the time-windowof opportunityfor suc- towering cumulusclouds or whenradar cell tops cessful intervention of the hail growthprocess is exceed20 kft height over the higher terrain along often less than 10 minutes. the western border on days whenthe forecast calls for thunderstormswith hail potential. 1998-99 FLIGHTSTATISTICS During the demonstrationproject of 1998-99,two Cloud top seeding can be conducted between hundredand ten (210) aircraft flights (515 flight -8°C and -15°C. The 20 g pencil flares fall ap- hours) were conducted on 64 days betweenthe proximately4000 ft (approximately10°C) during period Dec. 4th, 1998and March28th, 1999. Of their 35-40 s burn time. The seeding aircraft these, 161flights (437hrs) wereseeding flights, penetratethe edges of single convective cells and41 flights (66 hrs) werefor weathersurveil- meetingthe seedcriteria. For multi-cell storms,or lanceonly. Therewere 111 night time flights (286 storms with feeder clouds, the seedingaircraft hrs) and99 day-timeflights (229hrs). Thedistri- penetrate the tops of the developing cumulus bution of take-off andlanding times accordingto towers on the upshearsides of convectivecells, the time of day is shownin Figure2. as they growup throughthe -10°Caltitude. SEEDINGMATERIALS Cloud seeding was conducted on 52 days. The seedingconsisted of 18,480 droppable/ejectable ¯ Silver-iodide is dispensedusing droppable and/or flares (369,600gm seeding material), 2,015 burn- end-burning pyrotechnics. Acetonegenerators in-place flares (302,250gm seeding material), and were also used during the 1998-99 campaign, 642litres of acetonesolution (11,096gms
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