hydrometeorological significance of rime ice deposits in the colorado rockies

VOL. 19, NO. 4 WATER RESOURCES BULLETIN

AMERICAN WATER RESOURCES ASSOCIATION AUGUST 1983

HYDROMETEOROLOGICAL SIGNIFICANCE OF RIME ICE DEPOSITS IN THE COLORADO ROCKIES’

Edward E. Hindman, Randolph D. Borys, and Paul J. DeMott2

ABSTRACT: Observations and measurements were made during storm periods at mountain top sites in the Colorado Rockies during the winter of 1981-1982. On average, liquid clouds occurred with and without snowfall for, respectively, 75 percent and 15 percent of the observations. On average, the rime ice deposition rates were measured to be seven times the precipitation rates. The rime deposits were estimated to contribute 10 percent to the water content of the snowpack. Com- bining this figure with the estimated rime deposits on falling snow crystals (up to 50 percent by mass), up to 60 percent of the water content of the annual snowpack in the mountains near Steamboat Springs, Colorado, could be due to rime ice deposits. (KEY TERMS: rime ice deposits; icing deposits; water content of ice deposits; rime rates; snowfall rates; subcooled liquid cloud frequency.)

INTRODUCTION Liquid droplets frequently coexist with ice crystals in winter

mountain clouds. The clouds often form on upwind slopes with bases lower than the mountain peaks. In these situations, the supercooled droplets travel through the high elevation forests enveloping the forests in a fog. The needles on the pine trees are excellent collectors for the droplets. Consequently, many of the droplets freeze upon pine needles, and form a white deposit called rime ice. In certain wind speed, temperature, and cloud liquid water content situations, glaze ice forms instead, as detailed by Makkonen (1981).

When the temperature of the cloud is warmer than O°C, the droplets do not freeze. Instead they coalesce on the needles to form large drops which fall to the ground. This phenomenon is called “fog drip.” Parsons (1960) reports that up to 25 cm of “fog drip” can occur during the precipitation void summer months beneath Monterey pines and eucalyptus trees on the crest of the Berkeley Hills near San Francisco Bay. According to Wozniak (1975), in some mountain regions (presumably in nothern Finland), approximately 50 percent of the available water may originate from rime deposits and fog drip. Lovett, et al. (1982), report a similar value for subalpine forests in the northeastern United States. Further, Meaden (1979) argued that routine measurements of gIaze/rime collections and fog drip should establish the benefits of these deposits to the ecology. Finally, in situations where fog drip does not occur,

Burton (1971) has shown that dew formation is a source of moisture for coastal redwood trees.

Hindman and Grant (1981) have shown that, for the period February-April 1981 at Vail and Steamboat Springs, Colorado, rime ice deposits occurred at high elevations during most snowfall periods. Further, they report that, on average, at Steam- boat Springs, the rime rates were 10 times greater than the precipitation rates, a result consistent with values from Fin- land (Makkonen, 1981).

As a result of these findings, a more extensive study was initiated of the rime ice phenomenon in the Colorado mountains during the winter of 1981-82. Rime measurements were made by cooperating ski patrol personnel at Vail (Eagle’s Nest Ridge, 3048 m MSL), Steamboat Springs (Storm Peak, 3 156 m MSL), Berthoud Pass (chairlift top, 3662 m MSL), and Wolf Creek Pass (poma lift top, 3581 m MSL). Further, a mountain top laboratory was established at the summit of Storm Peak at Steamboat Springs where the authors conducted detailed rime ice investigations. The facility is referred to as Storm Peak Laboratory (SPL).

In this paper, it is shown from the 1981-82 data that: 1) liquid clouds occurred frequently during snowfall periods; 2) the rime rates, on average, were seven times the precipitation rates; and 3) the rime ice deposits on the mountain surface and on snow crystals were estimated to contribute 10 percent and 50 percent, respectively, to the water content of the snowpack. This paper is a revised and expanded version of Hindman, et al. (1982).

INSTRUMENTATION The rime measurements at Wolf Creek Pass (WCP) in the

southern Colorado Rockies, at Vail and Berthoud Pass (BP) in the central Colorado Rockies and at Steamboat Springs (SBS) in the Northern Rockies were made using a procedure detailed by Hindman and Grant (1981). Briefly, a 6.2 mm diameter wood dowel was exposed at eye level to the cloud at a location where the airflow was unobstructed. One measurement each of the width and depth of rime ice deposited during a period (-30 min) were obtained at the end of the period

Paper No. 821 23 of the Water Resources Bulletin. ‘Respectively, Research Scientist, Research Associate, and Ph.D. Student; Department of Atmospheric Science, Colorado State University, Ft. Collins,

Colorado 80523.

WATER RESOURCES BULLETIN 81 9

Hindman, Borys, and DeMott

(Figure 1). The wind speed and temperature were measured at the beginning and end of each period. Further, the observer recorded whether or not it was snowing and if liquid cloud was present at the beginning and end of each period. These measurements and observations were taken daily at each site by the cooperative observers.

The detailed rime ice measurements made at SPL during the winter of 1981-82 included the following. First, a Ro:e- mount icing Detector (Tattleman, 1982; Henderson and Solak, 1983) was operated. It provided a continuous record of icing periods and icing rates. Second, rime ice densities were estimated by exposing a preweighed 2 mm diam. dowel to the subcooled liquid cloud for five-minute periods. The subse- quent rectangular ice deposit was measured to determine the volume and the dowel was reweighed to determine the mass of the deposit. The density values were determined by divid- ing the mass by the volume. Third, a 6.2 mm dowel was exposed following procedures used by the cooperative observers to cross check the SPL measurements with those of WCP, Vail, and BP. Additional 6.2 mm dowels were placed at three lower sites (3048, 2745, and 2438 m) to determine the vertical ex- tent of rime ice deposits on the windward slopes of Storm Peak. The rods were inspected every morning. Fourth, cloud water measurements were made using the roto-rod device described by Rogers, et al. (1983). A spinning wire accu- mulated rime for a short period. The rime deposit was carefully removed from the wire and weighed. The mass of rime is related to cloud liquid water content (LWC) in g m-3. Ac- cording to Rogers, etal. (1983), LWC values from the roto rod vary * 50 percent from LWC by integrating simultaneously obtained droplet spectra (a more accurate method). The relationship for roto-rod LWC was derived in winter mountain clouds in the Wyoming Rockies and therefore, should be valid for use at SPL, where clouds with similar microphysical properties occur. Fifth, cloud droplet spectra were obtained using a cloud gun (Squires and Gillespie, 1952) as well as an active scattering and an axially scattering spectrometer probe (Knollenberg, 1976; Dytch and Camera, 1976). Finally, a

small branch was cut off an Engelman spruce (Picea Engel- mannii) near SPL to estimate the amount of rime ice a tree might collect. The branch was weighed prior to exposure to the airstream and reweighed approximately every hour to measure the integrated rime accumulation.

Rime ice and snowfall were collected separately at SPL using plastic collection devices for later chemical analyses. These analyses assessed the deposition of trace elements to the snowpack via direct cloud water interception by the mountain and via indirect deposition through ice crystal riming. The trace element properties of the rime ice and snowfall sam- ples and their significance to the deposition of acidic species have been reported (Borys, et al., 1982a, b).

PROCEDURES

The answers to the questions posed to the cooperative observers (Is a liquid cloud present? and Is it snowing?) were tabulated. Three categories were developed: 1) coexistence of liquid cloud and snowfall, 2) presence of only liquid cloud, and 3) absence of liquid cloud but snowfall occurring.

The rime ice deposition rates were calculated from the cooperative observer data and the data from SPL; the precipitation rates were calculated from 24-hour snowfall water equivalent measurements from the U.S. Forest Service (WCP, Vail, BP) and from the Steamboat Springs Ski Company. First, the liquid cloud and snowfall observations were examined for periods that had both liquid cloud and snowfall occurring at the beginning and end, and had an average wind speed 2 2.7 m s-1 (below this value the collection efficiency of the 6.2 mm dowel is difficult to define). Second, the 24-hour snowfall records were checked to verify that new snow was reported at the beginning and end of the 24-hour period. Third, the rime rates (R1, mm hr-l) were calculated using the following expression:

Figure 1. Rime Ice Depth (d=Smm) and Width (w=4min) Measurements Made on December 2, 1981, for a 30-Minute Period, 9 ms-l Average Wind Speed, -l l°C.

620 WATER RESOURCES BULLETIN

Hydrometeorological Significance of Rime Ice Deposits in the Colorado Rockies

where dl is the depth of the rime deposit (mm), p is the average density of the deposit, At is the collection period (hr), and e is the collection efficiency of the dowel as reported by Hind- man and Grant (1981). Macklin's (1962) laboratory relationship between accreted ice density ( p , g cm-3) and the median volume radius of the cloud droplet spectra (r, pm), the air speed (vo, m s-1) and the surface temperature of the ice (Ts, C) was tested using the corresponding measurements from SPL. It was found the relationship fit the SPL data with a small adjustment to compensate for the smaller r values (- 5pm) at SPL. The SPL relationship is

p = 0.165 (-r vo/Ts) 0.76

where -0.5 Q r vo/Ts < -10 and Ts was approximated by the air temperature. Accordingly, a value of 10 pm was used as the droplet median volume diameter in e determinations. Equa- tion (1) is accurate to +25 percent due to fluctuations in droplet spectra which affect p and e values. Finally, the precipitation rates (R2, mm hr-l) were calculated using the following expression :

R2 (mm hr-') = __ d2 24 hr.

(3)

where d2 is the water equivalent (mm) of the 24-hour snowfall accumulation. Values of R2 are good to f20 percent due to uncertainties in d2 values.

&me ice deposition rates were calculated from the Rose- ment measurements in the following manner. The rate of change of voltage from the sensor was transformed into a mass deposition rate (M, g s-1) using the relationship between voltage (V, volts) and mass (m, g) of Brown (1981) for the sensor used at SPL:

m = 1.9143 x 10-3V2 t 6.4756 x V - 0.008447(4)

Equation (4) is valid for 0.07 < V < 5.0. The rime deposition rate R1 was determined by combining M with the collection efficiency (e) of the sensor (identical to that of the 6.2 mm dowel) and the cross-sectional area of the sensor (2.54 cm x 0.62 cm) resulting in

R1 (mmhr-l) = 2.232 x 104M/e (5)

The e values were determined following the same procedure as with Equation (1).

The following procedure was used during a 15-minute period to obtain the rime ice measurements from the tree branch, the liquid water contents from the roto-rod, a cloud droplet sample, and an ice density measurement. First, the riming branch was photographed, the dowels were scraped clean of rime ice and the wind speed, direction, and air temperature were recorded. Second, the branch was carefully weighed. Third, the branch was reexposed to the liquid cloud

and the roto-rod device was exposed to the cloud. During the roto-rod exposure, a cloud gun sample was obtained. Fourth, the rime ice deposit on the roto rod was weighed. Finally, at the end of the period the wind speed, wind direction, temperature, and rime deposits on the dowels were measured. The rime deposit on the preweighed dowel was measured and weighed for density estimates. This sequence was repeated approximately every hour during a liquid cloud episode at SPL.

RESULTS

The results of the liquid cloud and snowfall observations from the cooperative observers are given in Table 1. The large number of observations at Steamboat Springs were primarily made by the authors at SPL. It can be seen from the table that large differences occurred in the incidence of liquid cloud at the various sites. At WCP and SBS, 95 percent and 90 percent of the observations during snowfall periods reported liquid cloud present, while at Vail and BP, 5 3 percent and 60 percent of the observations reported liquid cloud present. In contrast, Hindman and Grant (1981) report that 95 percent and 71 percent of the observations at Vail and SBS, respectively, during the winter of 1980-8 1 reported liquid cloud present. From these results, it is clear that rime ice occurred, on average, during 75 percent of the snowfall periods at exposed, high elevation sites at WCP, Vail, BP, and SBS. Also, it can be seen from Table 1 that liquid clouds occurred without snowfall, on average, during 15 percent of the observations during storm periods. Further, Judson (1971) reports frequent deposits of rime ice on Mines Peak (3808 m MSL) just 2 km to the east of the BP site.

The results of the rime rate and precipitation rate measurements are shown in Figure 2. Two significant features are ap- parent in the figure. First, the average rime rates for WCP, Vail, BP, and SBS are seven times the precipitation rates: 4.7 f 1.5 vs. 0.46 f 0.13 mm hr-1. This result is consistent with the result from Hindman and Grant (1981) for data from 1981 at SBS. Further, the precipitation rate value is consistent with measurements made by Feng and Grant (1982) at SBS. Second, although the regression equation in Figure 2 does not have a large correlation coefficient (r = 0.38) due to the scatter in the data, it appears that the rime and precipitation rates are positively correlated.

Observations and measurements were made typically once per day at WCP, Vail, and BP. As a result, it was necessary to assume that the rime and snowfall episodes occurred for the entire 24-hour period. Thus, the R1 and R2 values from these sites may be conservative. In contrast, at SBS, the measurements by the authors were nearly every hour, so the durations of the rime and snowfall episodes were accurately determined. Therefore, the SBS R1 and R2 values are considered accurate. Further, 10 simultaneous R1 measurements with the dowels and Rosemont sensor correlated (r = 0.79) and average R1 values were, respectively, 5.1 f 1.0 and 2.9 f 0.39 mm hr-l. It can be seen, in Figure 2, that the WCP, Vail, BP, and SBS

62 1 WATER RESOURCES BULLETIN


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TABLE 1. Percent of Observations Which Reported the Indicated Conditions.

Liquid Cloud Liquid Cloud and No Liquid Cloud Number of and Snowing Not Snowing and Snowing

Site Period Observations (percent) (percent) (percent)

Wolf Creek Pass 11/24/81 to 4/1/82 42 16

Vaii 11/26/81 to 4110182 53 28 Berthoud Pass 11/26/81 to 4/1/82 52 58 Steamboat Springs 11/30/81 to 4/1/82 24 1 I8

19 25 2

12

5

41

40

10

average R1 and R2 values are of the same order and, therefore, the WCP, Vail, and BP values are considered representative.

/

Figure 2. Rime Rates (R1) and Precipitation Rates (R2) From Wolf Creek Pass (WCP), Vail, Berthoud Pass (BP), and Steamboat Springs (SBS) for the Winter of 1981-82. The uncertainty in the values are given by the brackets about the WCP point. The linear regression equation relating (R1) and (R2) is given by the solid line:

Log R2 = 0.28343 Log R1 - 0.9293, r = 0.38

The results from one of the two test branch experiments are given in Figure 3. (Results from the 27-28 February 1982 experiment were similar to those in Figure 3.) Inspection of the figure reveals the following patterns: first, the branch ac- cumulated rime and the maximum value was reached when the cloud dissipated (the cloud period did not last long enough to determine if the branch became saturated with rime and shed rime); second, the branch lost rime after the maximum value was reached, due to wind buffeting and sublimation; third, the

rime rates were quite variable with initial high values; fourth, the rime densities were initially high, then decreased through the cloud period. The test branch was approximately 50 cm2 in cross-section area and weighed 33 g.

DISCUSSION The basic information has been assembled to estimate the

hydrometeorological significance of the rime ice deposits (Le., can they contribute to the water content of the snowpack?). The amount of water deposited to the snowpack by rime ice and precipitation was estimated in the following manner.

The rime ice measurements as a function of elevation at SBS revealed that, on average, the upper 400 m of Storm Peak was enveloped in liquid cloud during snowfall periods. The region of Storm Peak is approximately 70 percent covered with a mixture of Aspen and Engelman Spruce trees. Thus, the effective area impacted by the cloud was 400 m x unit width (m) x 0.70 or 280 m2. Observations of rime deposits in these forests by the authors indicate that the liquid cloud is collected by only the first few trees into the forest. Deep in the forest, no rime deposits were observed on the trees. Consequently, it is assumed that 100 percent of the cloud which flowed through these forests was deposited on the trees. The average rate of cloud water passing the summit of Storm Peak was measured to be 5.7 mm hr-1 (see Figure 2). The average density of the ice deposits was estimated using Equa- tion (2) to be 0.56 (r = 5pm,Yo = lOms-l, Ta = -1OC). Using these values, the rate of liquid deposition to the trees by rime ice on Storm Peak was on the order of.O.57 cm hr-1 x 2.8 x 104 cm2 x 0.56 g cm-3 = 8.9 x 103 g hr-1 or about 104 g hr-l.

The rate of liquid deposition to the trees by rime ice also was estimated from the test branch measurements. From Figure 3, it can be seen that 85 grams of ice were deposited during a 12-hour period. Following Thorne, et al. (1982), the collection efficiency of the needles on the branch was estimated to be - 0.5 (median volume drop diameter, 10pm and air speed of 15.6 m s-1). Therefore, the icing rate for the branch was 85 g + 12 hr f (50 cm2 x 0.50) = 0.28 g hr-1 cm-2. Using the same values for the effective area of trees on Storm Peak, the rate of liquid deposition to the trees was on the order of 0.28 g hr-1 cm-2 x 2.8 x 104 cm2 = 0.8 x 104 g hr-1, or about lo4 g hr-1. This result is consistent with the


Hydrometeorological Significance of Rime Ice Deposits in the Colorado Rockies

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11 FEB 82 + 1 z F E B 82

30 i700 2400 0600 1200 1800 2400 OGOO 1200 1800 2400 Oh00

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Figure 3. Rime Accumulation by a Test Branch on 9 and 10 February 1982 at SPL. The corresponding rime rates and rime densities are given as measured, respectively, with the 6.2 mm diameter dowel and 2 mrn diameter dowel.

results obtained from the rime rate measurements using the dowels.

Climatological records show the majority of the snowfall occurs within 25 km upwind of Storm Peak. Accordingly, the area affected by precipitation is 25 km x unit width (km) or 25 km2. The average precipitation rate in this area was assumed to be represented by the Steamboat value of 0.54 mm hr-1 (see Figure 2). The rate of liquid deposition to the surface by precipitation was on the order of 0.054 cm hr-l x 2.5 x 106 ern2 x 1 g em-3 = 1.4 x 105 g hr-1, or about 105 g

From the previous calculations, the rate of liquid deposition to the trees by rime ice was on the order of 104 g hr-l. The corresponding rate of liquid deposition to the watershed by precipitation was on the order of 105 g hr--l. Assuming all of the rime sheds from the trees to the snowpack, then the deposition of water due to precipitation is about 10 times greater than the deposition due to direct interception of cloud water by the mountain barrier. Consequently, 1 0 percent of the water content of the snow could be due to rime ice deposits and 90 percent due to snowfall. These results are similar to those of Berndt and Fowler (1969) and Gary (1972). For example, Gary measured the amount of rime ice whch fell t o the snow surface from Aspen trees in northern New Mexico and found it to be about 10 percent of the wintertime precipitation.

Feng and Grant (1982) measured the number flux of crystals and the corresponding precipitation rate (mm hr-l)

hr-1.

at SBS during the winter of 1981 and 1982. They show, for the same number flux of rimed and unrimed plates and planar dentrites, that the precipitation rate of the rimed crystals is, on average, twice that of the unrimed crystals. This result indicates that up to 50 percent of the water in the snow crystals could be from the rime ice deposits on the crystals. Com- bining this figure with the 10 percent value for direct rime deposits to the mountain results in a value of 60 percent. Up to 60 percent of the water content of the snowpack at SBS could be due to a combination of the cloud water collected by the trees and shed to the snowpack and the cloud water collected by the falling snow crystals.

CONCLUSIONS

Observations and measurements were made in subcooled liquid water clouds at mountain-top sites in the Colorado Rockies during the winter of 1981-82. The observations indicated that, on average, liquid clouds occurred during 75 percent of the snowfall periods at the sites. Liquid clouds occurred without snowfall, on average, during 15 percent of the observations during storm periods. The measured rime rates averaged seven times the precipitation rates. When the watershed areas affected by the rime ice deposits and snowfalls were considered, the calculated contribution of rime ice to the water content in the snowpack was estimated to be 10 percent. From these limited data, it appears that rime deposits on



trees, when they shed to the snow, may contribute about as Lovett, G. M., W. A. Reiners, and R. K. Olson, 1982. Cloud Droplet much water to the snowpack as appears possible from cloud seeding efforts (= 15 percent; Dennis, 1980). Finally, combining the results presented here with those of Feng and Grant (1982), it appears that up to 60 percent of the water content of the annual snowpack in the mountains east of Steamboat Springs, Colorado, could be due to rime ice deposits on high elevation trees (10 percent) and deposits on snow crystals (50 percent).

ACKNOWLEDGMENTS

The cooperative rime ice measurements were made by professional ski patrol personnel at Wolf Creek Pass, Vaii, Berthoud Pass, and at Steamboat Springs. The Steamboat Ski Corporation is acknowledged for logistics support for the Storm Peak Laboratory and the other CSU instrument sites on the ski area. Snowfall data were provided by the Avalanche Warning Center of the U.S. Forest and Range Experiment Station, Ft. Collins, Colorado. This study was a portion.of the research sponsored by NSF Grant ATM 8109590.

LITERATURE CITED

Berndt, H. W. and W. B. Fowler, 1969. Rime and Hoarfrost in Upper- Slope Forests in Eastern Washington. J . Forestry 67 :92-95.

Borys, R. D., P. J . DeMott, and E. E. Hindman, 1982a. The Relation- ship Between Ice Crystal Riming and the Trace-Constituent Com- position of Snow. Ppts. Conf. on Cloud Physics, Am. Meteor. SOC., Boston, Massachusetts, pp. 61-62.

Borys, R. D., P. J. DeMott, and E. E. Hindman, 1982b. The Significance of Snow Crystal and Mountain Surface Riming to the Removal of Atmospheric Trace-Constituents From Cold Clouds. Proc. 4th Conf. on Precipitation Scavenging, Dry Deposition and Resuspension, Elsevier, North Holland (in press).

Brown, E. N., 1981. An Evaluation of the Rosemont Ice Detector for Aircraft Hazard Warning and for Undercooled Cloud Water Content Measurements. NCAR-RAF Tech. Note, Boulder, Colorado, 9 pp.

Burton, R. E., 1971. A Weatherman Looks a t the Redwood Tree: Cali- fornia’s “Fog Drinker.” Weatherwise 24 :120-124.

Dennis, A., 1980. Weather Modification by Cloud Seeding. Academic Press, New York, New York.

Dytch, H. E. and N. J. Carrera, 1976. Cloud Droplet Spectrometry by Means of Light-Scattering Techniques. Atmos Tech. 8:lO-16.

Feng, D. and L. 0. Grant, 1982. Correlation of Snow Crystal Habits, Number Flux and Snowfall Intensity from Ground Observations. Ppts. Conf. on Cloud Physics, Am. Meteor. SOC., Boston, Massachu- setts, pp. 485487.

Gary, H. L., 1972. Rime Contributes to Water Balance in High-Eleva- tion Aspen Forests. I. Forestry 70:93-97.

Hindman, E. E., R. D. Borys, and P. J. DeMott, 1983. Hydrometeoro- logical Significance of Rime Ice Deposits on Trees in the Colorado Rockies. Proc. Intl. Symp. on Hydrometeorology, American Water Resources Association (in press).

Hindman, E. E. and L. 0. Grant, 1981. Utility of Mountaintop Rime- Ice Measurements. Ppts. 2nd Mt. Meteorology Conf., Am. Meteor. SOC., Boston, Massachusetts, pp. 404408.

Supercooled Liquid Water Concentrations in Winter Orogaphic Clouds From Ground-Based Ice Accretion Measurements. J. Wea. Modif. 15 :64-70.

Judson, A., 1971. An Infrared De-Icing Unit for Cup Anemometers. USDA Forest Service Research Note, RM-187,4 pp.

Knollenberg, R. G., 1976. Three New Instruments for Cloud Physics Measurements. Ppts. Intl. Conf. Cloud Physics, Am. Meteor. SOC., Boston, Massachusetts, pp. 554-561.

Henderson, T. J. and M. E. Solak, 1983.

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Deposition in Subalpine Balsam Fir Forests: Hydrological and Chemical Input. Science 218:1303-1304.

Macklin, W. C., 1962. The Density and Structure of Ice Formed by Accretion. Quart. J. Royal Meteor. SOC. 88:30-50.

Makkonen, L., 1981. Estimating Intensity of Atmospheric Ice Accre- tion on Stationary Structures. J. Appl. Meteor. 20:595-600.

Meaden, G. T., 1979. The Quantitative Measurement of Fog and Rime Deposition Using Fog-Guages. Weather 34:384-390.

Parsons, J. J., 1960. “Fog Drip” From Coastal Stratus, With Special Reference to California. Weather 15:58-62.

Rogers, D. C., D. Baumgardner, and G. Vali, 1983. Determination of Supercooled Liquid Water Content by Measuring Rime Rate. J. Cli- mate Appl. Meteor. 22:153-162.

Squires, P. and G. A. Gillespie, 1952. A Cloud Droplet Sampler for Use on Aircraft. Quart. J . Royal Meteor. SOC. 78:387-393.

Tattleman, P., 1982. An Objective Method for Measuring Surface Ice Accretion. J. Appl. Meteor. 21 599-612.

Thorne, P. G., G. M. Lovett, and W. A. Reiners, 1982. Experimental Determination of Droplet Impaction on Canopy Components of Balsam Fir. J. Appl. Meteor. 21:1413-1416.

Wozniak, Z., 1975. An Attempt of Quantifying the Contributions of Water Coming from Fog Deposits in the Water Balance of the Kar- konoszy Mountains. Zesz. Probl. Postep. Nauk Roln. 162:311-327.

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