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A GENERALIZED STUDY OF PRECIPITATION FORECASTING

PART 2: A GRAPHICAL COMPUTATION OF PRECIPITATION

P. M. KUHN

Abstract

A graphical technique for estimating areal precipitation patterns associated with given contemporary charts of streamlines and isotachs and of moisture at four selected levels is developed from the basic physical considerations presented by Thompson and Collins [1]. Procedures are described for calculating the vertical velocity at four selected levels by a kinematic method. The vertical velocities obtained are combined with a graphical solution of Fulks' formula for the rate of precipitation from pseudo-adiabatically ascending air and a method is derived for calculating the 12-hour rate of precipitation. An areal comparison is made of computed and observed precipitation.

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P. M. KUHN

Abstract

Measurements of the effective long-wave emissivity of clouds, equivalent to one minus the slab transmissivity, are obtained through thermal energy relations at cloud tops and bases after the manner of Gergen. Radiometric measurements are employed. Aircraft-verified cloud heights and measured effective cloud emissivities provide a basis for determining the presence of middle and high clouds. Such clouds result in large changes in radiation flux and apparent earth temperature measurements from satellites and high level balloons.

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P. M. Kuhn

Abstract

Employing 211 nocturnal radiometersonde observations of upward upward infrared flux, air temperature, and relative humidity in the atmosphere, the water vapor flux emissivity as a function of optical depth has been determined. The principal results of this study are:

(a) A new curve of water vapor flux emissivity, obtained from “in situ” atmospheric measurements, is compared with previous work. The emissivities are most reliable for optical depths typical of the troposphere as most of the data were obtained in those levels. One low stratospheric ascent made possible the measurement of a few values at low pressure and very shallow optical depth.

(b) When calculating infrared radiative flux in the atmosphere from temperature, humidity and pressure data, the accuracy will be improved if a pressure-reduced optical depth of (p/p 0).85 is used.

(c) There is evidence will be improved if a presure-reduced optical depth ratio will not serve over a wide range of optical depths, including both the stratosphere and troposphere But no further work would be profitable until more statospheric ascents at very shallow optical depths are available.

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P. M. KUHN

Abstract

Further data are presented to indicate the accuracy of the airborne economical radiometer (frequently termed radiometersonde when used in a modified radiosonde system) in the measurement of infrared radiation, in view of its recent widespread use. Three aspects are discussed. The first deals with a nocturnal ground comparison of the economical radiometer with a Suomi ventilated radiometer. The second covers an analysis of random errors in the net radiation obtained with the economical radiometer in the radiometersonde system. And, finally, an experimental in-flight verification of the correctness of the conductivity term in the equations for the economical radiometer is discussed.

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A. Shlanta and P. M. Kuhn

Abstract

The local ozone concentration and water vapor overburden were measured from a WB-57F aircraft near thunderstorms that reached or penetrated the tropopause. Two storms were studied extensively: one that penetrated 800 m above the tropopause and another that reached to about the tropopause level. In both cases, water vapor overburdens above and downwind averaged some 40% higher than those upwind of the storms. The water vapor overburdens directly above the higher storm were about 2.4 times that of those background measurements upwind and at the same levels; directly above the weaker storm the water vapor was about 1.8 times as great as the background measurements. The spatial distribution of ozone around the two storms was similar to that of the water vapor: downwind concentrations exceeded those upwind at all levels. An excess in ozone of about 25% was observed in circumnavigations above the storm tops when compared with fair-weather values at the same levels away from the storm. Ozone concentrations directly above the higher storm, however, were observed to be about 40% more than those concentrations away from the storm, while those directly above the weaker storm were about 20% less than in undisturbed air. It thus appears that thunderstorms do inject substantial amounts of water vapor into the stratosphere and that growing, electrically active storms also generate ozone at their tops.

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P. M. Kuhn and L. P. Stearns

Abstract

No abstract available.

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P. M. Kuhn and L. P. Stearns

Abstract

A radiometric method for the retrieval of moisture data at altitudes above the radiosonde hygristor cutoff region or in situations where a malfunction of the hygristor occurs is described. The method was applied to BOMEX radiation soundings. Regardless of the exact moisture profile, the method is designed to radiometrically infer the average decrease of moisture through the entire atmospheric column through a solution of the radiative transfer equation. This enables recovery of the total mass of atmospheric water vapor.

In at least 25% of all BOMEX radiometersonde ascents, humidity retrieval did produce a more realistic moisture profile and total mass of precipitable water vapor. In these cases, the radiosonde hygristor humidity deficiencies averaged from −45% at 800 mb to −30% at 600 mb. For such pressure levels, the optical mass of water vapor retrieved for the soundings discussed averaged 1.68 gm cm−2. This represents 56% of the hygristor-measured optical mass. Above 400 mb the optical mass recovered averaged 0.7 gm cm−2 for all BOMEX radiometer soundings. It is suggested that a simple radiometer could be used to improve moisture measurements for soundings requiring the best possible water vapor data.

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P. M. Kuhn and L. P. Stearns

Abstract

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P. M. Kuhn and V. E. Suomi

Abstract

A conventional Eppley Pyrheliometer was converted into a beam reflector by mounting it, upright, in the prime focus of a parabolic mirror. This unit, attached to an aircraft, provides a means of obtaining reflected short-wave radiation from small areas such as fields, cities, lakes, etc. Results of albedo measurements over parts of South Dakota, Iowa, and Wisconsin are given.

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D. O. Staley and P. M. Kuhn

Abstract

Balloon-borne radiometers were used to measure infrared radiative cooling through two intense, dry baroclinic zones in the middle troposphere. In both cases, a warming peak was associated with the baroclinic zone, with cooling of 2 or 3 deg C per day below and above. In one case, the warming peak was near the base of the zone; in the other, it was centered on the zone, although exact positioning of the peaks is uncertain because of the limited resolution of the radiometer in passing through the thin zones. In one of the two cases, upward radiative flux gradually increased upward above the baroclinic zone, although air temperature decreased upward. A probable explanation is lateral drift of the instrument past orographic clouds. The result calls attention to the limitation of the balloon-borne radiometer to use in situations of horizontally homogeneous surface and atmospheric radiative fluxes, and it indicates that upward radiative flux as measured from earth satellites may not agree closely with measurements from balloon-borne radiometers. The region of radiative destabilization within the baroclinic zone in one of the measurements coincides with the region of potential vorticity decrease as measured in a similar baroclinic zone. A decrease of cooling is noted as the tropopause is approached from below, in agreement with other measurements and with theory.

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