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  • Author or Editor: E. F. Danielsen x
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E. Paul McClain
and
Edwin F. Danielsen

Abstract

The thermal structure of the troposphere and lower stratosphere during the movement eastward of several Pacific troughs is examined primarily from the standpoint of the distribution of baroclinity within a vertical plane extending across the northwestern and north central United States. Baroclinity is defined and then expressed in a form suitable to the potential-temperature cross-sections employed in this study. Dominating features of the thermal field are two types of baroclinic zones: (1) broad and essentially non-frontal zones which form the leading and trailing edges of deep, rapidly moving cold domes in the middle and upper troposphere; (2) narrow, frontal type zones comprising the leading or trailing edges of either slowly-moving, low-level cold domes or rapidly-moving, upper-level ones. There is evidence that the non-frontal baroclinic zones are equally as important, both dynamically and synoptically, as the frontal ones.

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E. F. Danielsen
and
R. T. Duquet

Abstract

A machine method for computing winds from radiosonde and GMD-1 rawin tracking data is developed and the resulting winds are compared to those computed from precision FPS-16 radar tracking data. A direct comparison is possible because the measurements were made simultaneously by tracking the same effective target, which for the FPS-16 was metallic chaff in the balloon that carried the radiosonde transmitter.

With GMD measurements 10 times min−1 instead of the usual 1 min−1 and when elevation angles are >10°, the computed winds and ascent rates reproduced both the macroscale and mesoscale features derived from the FPS-16 data. The mesoscale features which have vertical wavelengths from 1.5–3 km include oscillations in wind direction and speed. When the elevation angles are <10°, the GMD antenna is misdirected by indirect signals reflected from the ground and large spurious oscillations and steps appear in the elevation angle measurements. It is impossible to recover the mesoscale winds from these erratic measurements, but the macroscale or synoptic scale winds can be obtained by fitting a low order polynomial to the entire set of low elevation angle measurements.

The winds computed from the FPS-16 measurements contain, between the earth's surface and the maximum altitude reached by the radiosonde balloon, many oscillations in wind speed and direction. The hodographs suggest that the velocities can be decomposed into a mean wind vector and a perturbation vector which rotates cyclonically or anticyclonically with height. In the stratosphere, anticyclonic rotation predominates. The perturbation vectors have magnitudes ranging from 0.5–10 m sec−1 and rotate through 2π rad in 0.5–3 km.

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E. F. Danielsen
,
R. Bleck
, and
D. A. Morris

Abstract

A one-dimensional, time-dependent numerical model of a cumulus cloud is presented that generates hail and radar reflectivities at realistic rates. The distribution of hydrometeors evolves with time as a result of condensation, sublimation, stochastic collection through collision and coalescence, sedimentation, drop freezing, and drop breakup. A total of 40 mass categories, each twice the mass of the former, corresponding to radii from 2.5 μm to 2 cm, are used to determine the ice and hail distribution. The first 31 categories up to a radius of 2.5 mm are used for the water drop distribution. Radar reflectivities are computed from Mie scattering theory for water and ice spheres in each category, then summed to give the reflectivities that can be compared to those observed by radar. Only the updraft radius at the earth's surface, the mixing coefficients, and the initial droplet distribution at cloud base are arbitrarily specified. Four initial droplet distributions are studied separately to determine their effect on hail growth rates and the water drop and hail distributions.

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R. T. Duquet
,
E. F. Danielsen
, and
N. R. Phares

Abstract

The distribution of wind and of temperature in a vertical cross section through the atmosphere is derived from radiosonde and rawinsonde data by an objective analysis procedure suitable for automatic computers. The method of interpolation takes advantage of the fact that soundings in the plane of the gross section provide data along vertical lines rather than at randomly distributed points. The thermal wind equation is used to modify the interpolated distribution through a partial differential equation derived from the calculus of variations. Results indicate that the technique is capable of delineating not only the gross vertical structure of the atmosphere but also some significant layers of high stability and/or potential vorticity which are inadequately defined by analyses in quasi-horizontal planes at the standard pressure levels.

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