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In-flight microphysical measurements in classical freezing-rain conditions were used to study the vertical and horizontal characteristics of the precipitation and associated low-ceiling, stratiform clouds, which are usually present as overcast in freezing-rain conditions. The low overcast is usually based in the surface cold layer but may extend up into the inversion, or transition layer, between the overrunning warm air and the surface cold layer. This gives the cloud an unusual temperature-inverted structure—supercooled in the lower half and warmer than freezing in the upper half. The low cloud is also subject to wind shear and turbulence that is due to the warm overrunning. The apparent effects of this are 1) increased cloud droplet concentrations in clusters up to a few hundred meters wide that occur sporadically in the cloud layer, 2) possible forcing of cloudy air upward from lower levels against the resistance of the temperature inversion and into the transition layer, and 3) highly variable air temperatures during level flight in the inversion layer.

About 28 000 nautical miles (n mi) of select in-flight measurements of liquid water content (LWC), droplet sizes, temperature, and other variables in supercooled clouds from a variety of research projects over portions of North America, Europe, and the northern oceans have been compiled into a computerized database for obtaining new statistics on the ranges, frequency of occurrence, and interrelationships of the variables. The LWCs are averaged over uniform cloud intervals of variable length. LWC probabilities are then generated as a function of averaging distance, temperature, droplet mass-median diameter (MMD), altitude, and freezing-level height. These variously scaled LWCs (different averaging intervals from 1 s to 200 n mi) are easily accommodated by distance-based graphing (LWC versus averaging distance). These graphs provide realistic LWCs for modeling, and they can serve as a common reference for comparing LWC measurements over any averaging scale. Maximum recorded LWCs are about 1.6 g m−3 in stratiform clouds and about 5 g m−3 in convective clouds, both over short (

A simple, new, triple-calibration scheme is developed for Goodrich (formerly Rosemount) model 0871FA ice detectors. The analog output voltage is equated not only to the usual liquid water concentration, but to accurately computed ice mass-and-depth accretion rates on the sensitive element of the detector. The three different calibration constants vary from detector to detector, but are related through invariant equations that are probe-independent. Thus, the relations can serve as universal calibration equations for any 0871FA detector. The method is demonstrated for three detectors in the steady-state conditions of an icing wind tunnel. Other observed characteristics of 0871FAs are described to help users understand the behavior of these detectors during operation

This work is a continuation of the previous climatological study of freezing precipitation and rime over the USSR territory [Bezrukova, N.A., Minina, L.S., Naumov, A.Ya., 2000. Freezing precipitation climatology in the former European USSR. Proceedings of the 13th International Conference on Clouds and Precipitation, pp.737-739, Reno, Nevada, USA, 14-18 August 2000; Bezrukova, N.A., Jeck, R.K., Minina, L.S., Khalili, M.F., Stulov, E.A., 2004. 10-year Statistics on Freezing Precipitation across the former USSR from surface weather observations. Proceedings of the 14th International Conference on Clouds and Precipitation, pp.731-734, Bologna, Italy, 19-23 August 2004.] aimed at creating an atlas of the frequency of these phenomena. This study gives considerable information about and a statistical analysis of freezing precipitation and rime events observed over the territory of the former USSR during a decade (1981-1990) and over the European territory of the USSR during two decades (1971-1990). This paper intends to draw the attention of the reader to the atlas and statistics by showing some interesting points. The authors used the data provided by the ground-based weather stations involved in the international exchange of meteorological data. The USSR network's Monthly Meteorological Tables (1971-1990) [Monthly Meteorological Tables, 1971-1990. Part 1, Novosibirsk-Obninsk. (in Russian).] comprising selected daily ground-based meteorological observations from more than 220 stations served as a basis for the analysis. All the types of freezing precipitation (FP) events were given as WMO Codes 56, 57, 66, 67, 24 and freezing fog (FF) deposited rime as WMO Codes 48, 49. The entire territory was divided into six major regions: the Arctic, the European part of the USSR, the TransCaucasus, Central Asia, Siberia, and the Far East. The frequency and distribution of events by regions versus temperature, atmospheric pressure, clouds base height, and some other meteorological parameters concerned were obtained. Climatic maps of annual mean, monthly mean, and seasonal mean occurrences of FP and FF were constructed for these regions. The study also analyzes the space-time variability of monthly mean ice-coating duration in hours for the 20-year period of 1971-1990 as observed at over 80 stations in the European part of the USSR (ET), and climatic maps of annual mean and monthly mean ice coating duration for the ET are constructed. The correlation between ice coating duration and height has been evaluated.

Radiosonde and surface observations in freezing rain (ZR) and freezing drizzle (ZL), and a limited number of aircraft measurements in ZR, have been examined for information on the magnitude and altitude dependence of meteorological variables associated with aircraft icing in these conditions. The variables include temperature aloft, humidity (clouds), and windshear from the radiosondes; surface temperatures, ceiling heights, precipitation type and amount from the surface observations; and temperature, dropsize, rainwater concentration, and icing rate from the instrumented aircraft. These and other data are used here to arrive at tentative maximum and representative values of these variables. To overcome the inadequacy of median volume diameter (MVD) as a measure of dropsize for these large droplet conditions, a convention for reporting the ZR or ZL water concentration over a few coarse dropsize intervals is proposed.

Radiosonde temperature and humidity data were used to deduce the vertical distribution of clouds and aircraft icing conditions near Washington, D.C. when low ceilings occurred with surface temperatures near freezing. Twenty-three soundings from 12 cold, low ceiling episodes during the winter of 1981/82 were examined for this study. Results indicate the following: (a) generally, a deep, apparently unbroken cloud layer existed above the low ceilings; (b) typically, a cold surface layer existed under a relatively strong inversion; (c) while icing conditions above the cold, low ceilings are mitigated by inversion or isothermal layers, 70% of the cases still required flight into significant icing conditions; and (d) local geographic effects can noticeably influence ceiling height and visibility. Automated predictions of the icing probability, type, and.severity were generated from the radiosonde data and were supplemented with pilot reports; reasonable agreement was found.

Most of the principal airborne cloud-physics projects during the ten-year period 1974-1984 are documented to provide selected information on the type and quantity of microphysical data that have beencollected. The emphasis is on measurements above the melting levelwhere over 2100 flights from 55 different projects have taken place.Most (1825) flights are from the United States and Canada, but 319are from various locations around the world. The number of flightswith data on liquid-water content, droplet sizes, ice particles, snow,and other hydrometeors are tabulated.