Freezing Precipitation Research Articles

北海道を事例にしたClimate Severity Indexと主成分分析結果の比較

In cold region like Hokkaido, severity index evaluated by weather conditions and sense of climate in each area is required for defining winter's misery. 1) When assuming total hours of snowstorm or freezing precipitation in case of Japan, climate severity index (CSI) in Hokkaido can be calculated. CSl in Hokkaido had a range from 32 to 50. 2) Six levels of adaptation to winter defined by N. Pressman were asked to staffs of promotion section of Cities in Hokkaido and to two groups of students in Hokkaido University as a questionnaire. Replies of enduring winter were the most among the six levels. Reply pattern of each group to the six levels was very similar. 3) Regional climate map (Hokkaido) was proposed by using coefficient from principle component analysis. The analysis used data of questionnaire results to officials of Hokkaido Government and of weather condition. Regional climate map was well relative to CSI.

Model Representation of Freezing and Melting Precipitation: Implications for Winter Weather Forecasting

Abstract During episodes of sustained moderate or heavy precipitation in conjunction with near-freezing temperatures and weak horizontal temperature advection, the latent heat released (absorbed) by the freezing (melting) of falling precipitation may alter thermal profiles sufficiently to affect the type and amount of freezing or frozen precipitation observed at the surface. Representation of these processes by operational numerical weather prediction models is incomplete; forecaster knowledge of these model limitations can therefore be advantageous during winter weather forecasting. The Eta Model employs a sophisticated land surface model (LSM) to represent physical processes at the lower-atmospheric interface. When considering the thermodynamic effect of melting or freezing precipitation at the surface, it is shown that limitations in the current version of the Eta LSM can contribute to biases in lower-tropospheric temperature forecasts. The Eta LSM determines the precipitation type reaching the surface...

A Synoptic Weather Pattern and Sounding-Based Climatology of Freezing Precipitation in the United States East of the Rocky Mountains

Abstract An analysis of 411 winter storms that produced freezing precipitation events in the United States east of the Rocky Mountains over the 25-yr period of 1970–94 is presented to identify specific weather patterns associated with freezing precipitation and to determine their frequency of occurrence. Seven archetypical weather patterns are identified associated with freezing precipitation. Four patterns (arctic fronts, the warm front–occlusion sector of cyclones, cyclone–anticyclone couplets, and the west quadrant of anticyclones) are not associated with specific topographic features. Three patterns (East Coast cold-air damming with an anticyclone, cold-air damming with a coastal cyclone, and cold-air trapping during approaching continental cyclones) are associated with freezing precipitation in and along the Appalachian Mountains. The frequency of occurrence and duration of each of these patterns are presented, and variability within patterns is discussed. In the second part of the paper, the vertica...

Regional and Local Influences on Freezing Drizzle, Freezing Rain,and Ice Pellet Events

Regional and local influences on frequency and type of freezing precipitation (freezing drizzle, freezing rain, and ice pellets) are investigated via in-depth climatologies of six continental United States (CONUS) sounding sites. For each site, wind roses of precipitation type occurrences are compared with those for nearby stations and the aggregate values for the CONUS. Synoptic scenarios and sounding structures are identified for prolonged events of each precipitation type and probable formation mechanisms are discussed. Station location relative to topographic features smaller than 1 km in height, water bodies ranging in size from oceans to small bays, and dominant wintertime storm tracks are shown to play a major role in the determination of the frequency and type of freezing precipitation at each site. Results help to explain the regional maxima and minima of freezing precipitation across the CONUS, as well as the dominance of certain precipitation types and formation mechanisms in different portions thereof. Understanding these differences is necessary for proper development of techniques used to diagnose and forecast surface precipitation type and the occurrence of hazardous aircraft icing conditions associated with freezing precipitation aloft.

A climatological study of surface freezing precipitation in Europe

AbstractA climatological study of the occurrence of freezing precipitation at ground level is presented. It is based on reports of freezing precipitation in SYNOP messages from the three winters covering the years 1995–1998. The geographical domain covered is Western and Central Europe, extending northwards to Scandinavia and southwards to North Africa. The types of freezing precipitation selected are freezing rain, freezing drizzle and ice pellets. The frequency of occurrence of each of these types of freezing precipitation was computed. The results show that freezing precipitation is not an uncommon phenomenon in Europe, with the combined frequency of the various types of freezing precipitation (either drizzle, rain or ice pellets) being 0.5 to 1% of all SYNOP messages that include an observation of the current weather in Central Europe. The surface air temperature intervals associated with freezing precipitation have been studied. An attempt was then made to determine the mode of formation of freezing precipitation (either by melting of snow crystals in a layer of positive temperatures or by a process of coalescence or diffusional growth) by studying the thermodynamic soundings associated with freezing precipitation events. Copyright © 2000 Royal Meteorological Society

The Relative Importance of Warm Rain and Melting Processes in Freezing Precipitation Events

The importance of warm rain and melting processes in freezing precipitation events is investigated by analyzing 972 rawinsonde soundings taken during freezing precipitation. The soundings cover regions of the United States east of the Rocky Mountain states for the period 1970–94. The warm rain process was found to be unambiguously responsible for freezing precipitation in 47% of the soundings. In these soundings, the clouds had temperatures entirely below freezing, or had top temperatures that were above freezing. Another 28% of the soundings had cloud top temperatures between 0° and −10°C. Clouds with top temperatures >−10°C also can support an active warm rain process. Considered together, the warm rain process was potentially important in about 75% of the freezing precipitation soundings. This estimate is significantly higher than the estimate of 30% in a previous study by Huffman and Norman. The temperature, moisture, and wind profiles of the soundings, their geographic distribution, and the common occurrence of freezing drizzle at the sounding sites suggest that most of these events were associated with shallow cloud decks forming over arctic cold air masses. The “classic” freezing rain sounding, with a deep moist layer and a midlevel warm (>0°C) layer, was observed in only 25% of the sample. In these soundings, the depth of the cloud layer implies that melting processes were important to precipitation production. From the geographic distribution, the common occurrence of freezing rain, and the sounding profile, these cases appear to be associated primarily with cold air damming and overrunning along the U.S. East Coast, and with warm-frontal overrunning in the midwestern United States.

Microwave Properties of Frozen Precipitation around a North Atlantic Cyclone

Abstract Microwave brightness temperatures emanating from a North Atlantic cyclone were measured by the Special Sensor Microwave/Imager (SSM/I) on the Defense Meteorological Satellite Program satellite. As other investigators have found before, low 85.5-GHz brightness temperatures (215 ± 20 K) were observed from cumulonimbus clouds along the squall line; however, 85.5-GHz microwave brightness temperatures observed from the nimbostratus clouds north of the low center were significantly higher (255 ± 20 K). In situ measurements from aircraft during the Canadian Atlantic Storm Program II showed that heavy snowfall consisting of large tenuous aggregates existed in the nimbostratus clouds at the time of the SSM/I overpass. Distributions of snow, rain, liquid cloud water, and cloud ice mass were computed from a modified version of the fifth-generation Pennsylvania State University–NCAR Mesoscale Model. That model employed a mixed-phase ice microphysics (MPIM) scheme that only considered one type of frozen hydro...

Surface weather features associated with freezing precipitation and severe in-flight aircraft icing

Surface observations of freezing precipitation and pilot reports of severe in-flight aircraft icing for the continental United States are compared to the location of surface weather features, including airmasses of different origin and position relative to fronts, low-pressure centers and troughs. Statistics are calculated to determine where freezing precipitation and severe aircraft icing occur most often, and are produced most efficiently (number of occurrences per unit area). Airmasses found along the east and west coasts of the US are the most efficient producers of freezing precipitation and pilot reports of severe icing, respectively, while the areas ahead of surface warm fronts are the most efficient producers of both of these phenomena. The weather conditions typically found in these locations, and others that are of interest for freezing precipitation and aircraft icing, are discussed.

Freezing Rain: An Observational and Theoretical Study

Abstract Data from a Doppler radar, an instrumented aircraft, and several rawinsonde observations during freezing rain and ice pellet events have been analyzed for this study. From these data, 34 soundings were obtained that characterized the vertical structure of the atmosphere at the time of the freezing precipitation. These soundings were analyzed to determine the general nature of the vertical structure and the environmental conditions common to these types of winter precipitation events. The state of the hydrometeors reaching the surface (i.e., supercooled liquid or ice) was critically dependent upon the melting and refreezing characteristics. To better understand these characteristics, two theoretical models were used: 1) a heat transfer model to simulate the melting of a dendritic snowflake and 2) a separate heat transfer model to simulate the refreezing characteristics of a liquid droplet. These two models were run using typical values for lapse rates and temperatures as determined from the soundi...

High-resolution snow-water equivalent measurement by gamma-ray spectroscopy

Frozen precipitation has important implications for water quality and soil biology. Nutrients in landspread animal manure are transported to surface waters by snowmelt, and winter survival of forages often depends on snow cover. Further development of mechanistic snow behavior models would be assisted by improved measurements of the disappearance of water from snowpacks. We developed a system to measure the total water content (snow-water equivalent, SWE) of a snow cover based on attenuation of γ-rays. A mixed Eu-152, 154 source (about 70 MBq) was pushed through raceways which were placed on the soil surface prior to snowfall. Attenuation of the emitted radiation by solid and liquid water in snow was measured with a Ge detector held above the snow and a multichannel analyzer. Use of four energy peaks and solution of the six resulting equations reduced dependence of the measurement on source-detector geometry. In laboratory tests, measurements of a fixed water depth (30 mm) were constant to ±1.5 mm following displacement of the detector by 50 mm laterally and 100 mm vertically, a much larger repositioning error than occurs in the field. Field tests showed that the system detected melting conditions with greater sensitivity than was attained with collecting of snow cores. Errors in estimated SWE due to repositioning of the detector were about ±3 mm. Estimated energy balance terms were in reasonable agreement with observed melting during a field experiment. The new device will allow non-destructive SWE measurements to assess the influences of a number of agricultural management practices on winter hydrology.

Warm frontal structure in association with a rapidly deepening extratropical cyclone

Abstract The detailed characteristics of a CASPII warm frontal passage are presented in this article. This storm, Intensive Operating Period (IOP) 13 (February 26–27, 1992), was observed in detail with an array of diverse instruments. It has the advantage over earlier freezing precipitation studies of having simultaneous, in situ and remote sensing measurements by aircraft and ground‐based Doppler radar. The associated precipitation was in the form of banded structures parallel to the front. Within these bands were embedded precipitation cores, some parallel to the band, some perpendicular. The warm front itself was characterized by major perturbations in its kinematic and thermodynamic features. The cores oriented parallel to the front were the result of embedded convection generated, at least in part, by the irregularities in the frontal surface. The cores oriented perpendicular to the front were closely associated with the 0°C isotherm on the underside of the frontal inversion. Precipitation phase chan...

Winter storms over Canada

Abstract Various type of winter storms occur over Canada and produce major impacts on society. Canada is subjected to extra‐tropical cyclones with all their embedded structures, as well as blizzards, mountain‐induced storms, lake effect storms and polar lows. Many of these storms are accompanied by heavy precipitation in the form of snow or freezing precipitation, bitterly cold conditions, strong winds, and blowing snow. The occurrence and nature of these storms are discussed in this review article.

The Supercooled Warm Rain Process and the Specification of Freezing Precipitation

Abstract About 30% of freezing precipitation cases are observed to occur in a subfreezing atmosphere (contrary to the classical melting ice model). We explain these cases with the concept of the “supercolled warm rain process” (SWRP): the warm rain process can yield liquid hydrometeors at subfreezing temperatures whenever too few ice nuclei are available to create solid hydrometeors. We find that all of the freezing precipitation cases in a subfreezing atmosphere show a rapid decrease of moisture content in the zone above the inferred cloud top (decreasing from liquid to ice saturation in lm than 20 mb), at temperatures ranging from 0° to −10°C. Additionally, this structure prevails among freezing cases (43%) much more than among solid or liquid cases (10% and 15%, respectivelly). Regression experiments demonstrated that freezing precipitation was best described when (discretized) predictors were combined to describe particular physical processes, such as the SWRP. Besides the SWRP, the usual melting ice ...

Freezing Precipitation in Winter Storms

The mesoscale storm structure and the evolution of precipitation type are examined during freezing precipitation episodes over southern Ontario. Precipitation bands linked to both warm and cold fronts were mainly responsible for the precipitation during these episodes. One feature detected by radar and related to freezing rain and/or ice pellets in most cases was the initial radar overhang. Observations of mixed precipitation types, including snow and ice pellets with freezing rain, are partially a consequence of size-dependent differences in melting and refreezing within an upper level invention and a lower level subfreezing region, respectively. Inadequate time for refreezing in the lower subfreezing region may, however, lead to particles at the ground being composed of a mixture of water and ice. Prediction techniques for this type of severe weather need to account for its mesoscale nature and for the actual types of precipitation involved.

Acidic precipitation: Considerations for an air quality standard

Acidic precipitation, wet or frozen precipitation with a H+ concentration greater than 2.5 μeq l−1, is a significant air pollution problem in the United States. The chief anions accounting for the H+ in rainfall are nitrate and sulfate. Agricultural systems may derive greater net nutritional benefits from increasing inputs of acidic rain than do forest systems when soils alone are considered. Agricultural soils may benefit because of the high N and S requirements of agricultural plants. Detrimental effects to forest soils may result if atmospheric H+ inputs significantly add to or exceed H+ production by soils. Acidification of fresh waters of southern Scandinavia, southwestern Scotland, southeastern Canada, and northeastern United States is caused by acid deposition. Areas of these regions in which this acidification occurs have in common, highly acidic precipitation with volume weighted mean annual H+ concentrations of 25 μeq l−1 or higher and slow weathering of granitic or precambrian bedrock with thin soils deficient in minerals which would provide buffer capacity. Biological effects of acidification of fresh waters are detectable below pH 6.0. As lake and stream pH levels decrease below pH 6.0, many species of plants, invertebrates, and vertebrates are progressively eliminated. Generally, fisheries are severely impacted below pH 5.0 and are completely destroyed below pH 4.8. At the present time studies documenting effects of acidic precipitation on terrestrial vegetation are insufficient to establish an air quality standard. It must be demonstrated that current levels of precipitation acidity alone significantly injure terrestrial vegetation. For aquatic ecosystems, current research indicates that establishing a maximum permissible value for the volume weighted annual H+ concentration of precipitation at 25 μeq l−1 may protect the most sensitive areas from permanent lake acidification. Such a standard would probably protect other systems as well.

Comments on “Verification and Further Development of an Operational Model for Forecasting the Probability of Frozen Precipitation”

Comments on “Verification and Further Development of an Operational Model for Forecasting the Probability of Frozen Precipitation”

Verification and Further Development of an Operational Model for Forecasting the Probability of Frozen Precipitation

Abstract An automated system for forecasting the conditional probability of frozen precipitation was put into operation by the National Weather Service in November 1972. The Model Output Statistics (MOS) concept was used to develop the system, and both teletypewriter and facsimile products have been distributed to field offices twice daily. In this paper, guidance forecasts from this system are compared to subjective (local) forecasts prepared at Weather Service Forecast Offices. The local forecasts have been archived since September 1973 as part of a combined aviation/public weather forecast verification program within the National Weather Service. The comparative verification between the guidance and locals for two different data samples shows the guidance has produced better forecasts for the 18, 30, and 42 h projections. In attempting to improve the operational system, we experimented with the Regression Estimation of Event Probabilities (REEP) screening technique. The operational system had been deve...

An Analysis of the Freezing Precipitation Situation of December 10–11, 1954

An Analysis of the Freezing Precipitation Situation of December 10–11, 1954