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<br />. .l t' ..,_.... ~.. .
<br />
<br />..'_ . ....~., t" .
<br />
<br />.' "
<br />
<br />(
<br />
<br />These results suggest that the
<br />precipitation conversion efficiency for these
<br />limited cases may be relatively low (Dirks,
<br />1973). The February cue in particular seems
<br />consistent with the low precipitation efficiency
<br />observed for a shallow orographic cloud system
<br />(Rauber and Grant, 1985). The lower efficiency
<br />of the February 9th case may reflect the warmer
<br />temperatures ( -130C) of the measurement levels,
<br />compared to the cooler flight level temperatures
<br />of the March 15 (-190C) and December 9th (-200C)
<br />ca ses. The somewhat higher va 1 ue for the
<br />December Cllse is consistent with the low cloud
<br />liquid water content values measured.
<br />
<br />{,
<br />(
<br />\
<br />
<br />~hic Influence On Distribution Of
<br />tlOUdl[iquid Mater
<br />
<br />The possible influence of lIOuntain
<br />topography on the distribution of cloud liquid
<br />water may have an impact on the desi gn of any
<br />future seeding experiments. To examine this, the
<br />geographical distribution of liquid water
<br />measurements were made for selected cases alon g
<br />the east-west aircraft flight track. Figure 3
<br />illustrates such a distribution for the
<br />March 24, 1983 case. A geographical
<br />cross-section of the mountain topography from the
<br />western to eastern endpoints of the fll ght line
<br />area is illustrated, and the locations of
<br />Cranbrook (YXC), Sparwood (WSW), Pincher Creek
<br />(ZPC) and the Continental Divide indicated. The
<br />cloud liquid water contents for one flight pass
<br />and the average for all flights are indicated
<br />above the topography where they were made.
<br />L i qui d water measurements were avera ged over
<br />every 0.1 degrees of longitude from west to east.
<br />
<br />2.4
<br />
<br />Ttlese measurements indicate a cloud mass
<br />generally to the west of the divide, with an
<br />isolated cloud complex at the eastern project
<br />edge. Some evidence of a linkage between
<br />increased liquio water amounts and elevated
<br />topography is indicated both in the single-pass
<br />plot and the averaged data. Peak liquid water
<br />va lues are indi cated upwind of the two hi ghest
<br />ranges. While these results are very limited,
<br />
<br />Eat-W.,t CkSInlM"'" 01 ~ul(! _Ie, -...~ 24. 11183
<br />
<br /> OJ'
<br />i eft
<br />I ..
<br />f
<br />!
<br />f
<br />i
<br />...
<br /> a#
<br /> ..,.,
<br />
<br />- ...-.p.r:......-c ......_.
<br />--- ....c..--.
<br />_T.......~-.;C
<br />
<br />
<br />zPC
<br />
<br />..."5
<br />
<br />_n'
<br />
<br />~-----'
<br />
<br />~
<br />
<br />Figure 3. East-west distribution of liquid water
<br />for March 24, 1983. Topography between Cranbrook
<br />British Columbia (YXC) and Pincher Creek Albert;
<br />(2PC) is indicated (distance is approxi~tely 150
<br />km).
<br />
<br />~~:
<br />
<br />they suggest that the local relief lllIy play an
<br />important role in the establishment of pocKets of
<br />supercooled liquid water upwind of barriers.
<br />This .c>uld be consistent with results recently
<br />reported for winter orographic clouds in central
<br />Utah (Lon g, !l..!l., 1985).
<br />
<br />3. COIl1.USIONS
<br />
<br />The recently initiated snow research
<br />effort has provided a prel iminary look at the
<br />potential for snow augnentation in the southern
<br />Canadian Rocky Mountains. L imitecl aircraft
<br />measurements, the first of their kind in Canada,
<br />indicate the presel'lce of liquid water in winter
<br />clouds over the mountains and a relatively low
<br />amount of naturally occurring ice crystals. In
<br />addition, estimates of cloud precipitation
<br />conversion efficiel'lcy suggest that some of these
<br />clouds may not be efficiel'ltly converting upwind
<br />water vapour. These results indicate that
<br />conditions favourable for cloud seeding may be
<br />present. The extent and frequency of available
<br />cloud liquid water remains unknown. al'ld the
<br />delineation of this necessary condition would
<br />have to be determined prior to a more confident
<br />assessment. This determination would require the
<br />use of other monitoring instrumentation such as a
<br />dual-channel microwave radiometer. A proposed
<br />future project ~uld attempt to extend these
<br />limited llleasurements and implement an intensive
<br />monitoring and assesslllent program.
<br />
<br />4. ACKIOLEDGEMENTS
<br />
<br />The authors would like to acknowledge and
<br />thank our colleagues at the Alberta Research
<br />Council. Most of the description of the aircraft
<br />system was provided by D. Rogers. INTERA
<br />Technologies Ltd. operated the research aircraft
<br />used during the winter field programs. Funding
<br />support by Alberta Agriculture, the Alberta Water
<br />Resources Commissio~ and the Alberta Research
<br />Council is gratefully acknowledged.
<br />
<br />5. REfERENCES
<br />
<br />Barlow, F.O, F.E. RObitaille and J.H. Renick,
<br />1985: Microphysical characteristics of
<br />winter cloudS in AlbertI, presented at
<br />Workshop on the Physics of Orographic
<br />Precipitatiol'l and its Modification, U.S.
<br />Bureau of Reclamation, Denver, Co lorado,
<br />October 1-3.
<br />
<br />Barlow, F.O., f.E. Robitaille, J.W. Mason,
<br />C.M. Sackiw, 1983: Snow Climatology of
<br />the southern Canadian Rock ies, Papers
<br />!Presented at 17th Annual CMOS Congress,
<br />ARC Report, 2-11.
<br />
<br />Cheng . L., E. Peake,D. Rogers. A. Davis, 1986:
<br />Oxidation of Nitric Oxide Controlled by
<br />Turbulent Mixing In Plumes From Oil Sands
<br />Extraction Plants. At~spheric
<br />Environment, (in press). -
<br />
<br />I
<br />t
<br />
<br />Dirks, R.A, 1973: The precipitation efficiency
<br />of orographic clouds, J. de Rech. Atmos..
<br />1, 177-184.
<br />
<br />II
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