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Stanley David Gedzelman

A weather-forecasting contest was conducted at the City College of the City University of New York during the spring semester of 1977. The backgrounds of the participants were such that it was possible to classify each as either “experienced” or “inexperienced” and as either “educated” or “uneducated.” An analysis of the contest results suggested that, provided there is a basic meteorological education, 1) a beginner acquires much of the weather-forecasting skill he will ever have after making about 30 detailed forecasts, and 2) there appears to be a rather small advantage to being meteorologically educated, but the sample size was too small to determine the statistical significance of the advantage. The value of experience is, however, quite important for the more unusual weather situations. It also appears that the amount of effort and time spent preparing forecasts is of great importance.

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Stanley David Gedzelman

Abstract

The stability analysis of baroclinic magnetic flow for an unbounded fluid with a linear profile is presented. An analytic expression for the stability boundary is found, corroborating the results of Gilman obtained for a confined fluid that there is neither a long wave cutoff for instability nor a maximum value for the magnetic field at which instability may occur. In the limit of vanishing magnetic field the results coincide with those obtained by Burger.

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Stanley David Gedzelman

Evidence from the drawings, experiments, and writings of Leonardo da Vinci are presented to demonstrate that da Vinci recognized and, possibly, discovered the downburst and understood its associated airflow. Other early references to vortex flows resembling downbursts are mentioned.

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Stanley David Gedzelman

Abstract

Gravity waves for the one year period beginning 19 October 1976 around Palisades, New York, are investigated to determine their statistical properties and sources. The waves have typical periods of 10 min, pressure amplitudes of 3 Pa and velocities of 30 m s−1. In general, the largest, amplitude waves occur during late fall and early winter when the upper tropospheric winds directly overhead are fastest and the static stability of the lower troposphere is greatest. Mean wave amplitudes correlate highly with the product of the mean maximum wind speed and the mean low level stratification directly aloft. A distinct diurnal variation of wave amplitudes with the largest waves occurring in the pro-dawn hours is also observed as a result of the increased static stability then.

The majority of waves are generated by shear instability; however, a number of waves are generated by distant sources such as nuclear detonations or large thunderstorms. The waves with distant sources can be distinguished on the basis of their generally much higher coherency across the grid and velocities that depart markedly from the wind velocity at any point in the sounding.

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Stanley David Gedzelman
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Stanley David Gedzelman

A brief outline of the history of cloud painting prior to the first cloud classification schemes of Luke Howard and Lamarck is presented. It is shown that European painters had accurately represented most of the different cloud forms between about 1425 and 1675.

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Stanley David Gedzelman and Michael Vollmer

We present simple radiative transfer models for the radiance and color of atmospheric optical phenomena. Skylight, halos, and rainbows are treated as singly scattered sunlight that is depleted by scattering as it passes through a plane-parallel atmosphere and a vertical rain shaft or a geometrically thin cloud layer. Skylight in a molecular atmosphere grades from deep blue at the zenith to pale blue near the horizon whenever the solar zenith angle φ sun ≤ 80°. Skylight near the horizon is orange resulting from wavelength-dependent scattering by air molecules and aerosol particles through a long oblique path through the atmosphere when the sun is low in the sky (φ sun ≥ 85°). Halos (and coronas) seen through clouds facing the sun are brightest for cloud optical depth τ cld ≈ cos(φ sun), and fade to obscurity for τ cld ≥ 5. Rainbows (and glories), seen by light that is backscattered from clouds, also appear most dramatic when 0.2 ≤ τ cld ≤ 1, but remain visible even in the thickest clouds.

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Stanley David Gedzelman and Robert Arnold

Abstract

A two-dimensional, parameterized kinematic cloud microphysics model is described and used to simulate the form of cyclonic precipitation and its thermal impact in three idealized situations. The first situation represents a strong, warm, or stationary front with a zone of freezing rain and ice pellets separating regions of rain and snow. The second represents a storm with initial surface temperatures slightly above 0°C, and in which precipitation at the ground changes from rain to snow as a result of cooling by melting and evaporation of hydrometeors. The third represents a shallow cloud in a sounding with all temperatures below0°C that initially produces freezing drizzle before a change to snow or ice pellets.

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Stanley David Gedzelman and Michael Vollmer

Abstract

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Stanley David Gedzelman and James R. Lawrence

Abstract

Precipitation samples were collected at stations in the Eastern United States for two extratropical cyclones during the Genesis of Atlantic Lows Experiment (GALE) of 1986 and analyzed for their δ18O values. They represent the first synoptic-scale datasets of isotopic values.

Measured isotope ratios are explained in terms of physical principles and meteorological processes. They are shown to be related to vertical profiles of ω cloud-top temperatures, evaporation beneath cloud base, isotope equilibration, and water vapor sources for the precipitation. Measured isotope ratios are then compared to values obtained from simple models of convective and stratiform precipitation.

Both storms are shown to exhibit a consistent pattern of isotope ratios, with lowest δ18O values occurring in the stratiform precipitation well within the cold air, and highest values associated with the convective precipitation of the warm sector. A pronounced-amount effect, in which δ18O values decrease as rainfall totals increase, is also identified at many stations. The isotopic datasets from these storms may prove useful in deriving physical calibrations for climatological relationships between mean annual surface temperature or precipitation amount and the δ18O value of its precipitation for both present and past climate patterns.

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