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J. M. Austin

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J. M. Austin

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J. M. Austin
and
Collaborators 1

The results of an empirical study of 500-mb patterns are presented. It is shown that the prediction of the 24-hr and 48-hr intensification or weakening of troughs and ridges can be aided by a consideration of upstream changes. Qualitative rules for the prediction of a 24-hr change in the speed of troughs and ridges are included. Finally a climatological summary is presented of intensification, weakening and speed of troughs and ridges.

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J. M. Austin
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Austin G. Clark
and
Daniel J. Cecil

Abstract

The Tropical Rainfall Measuring Mission (TRMM) Lightning Imaging Sensor (LIS) was used to investigate inter-annual variability of lightning from 1998-2014 within the 38° S – 38° N range. Previous studies have indicated that the El-Niño/Southern Oscillation (ENSO) phenomenon is one significant contributor to inter-annual lightning variability, potentially the dominant mechanism on the global scale. This period of 16 years contained 4 warm- (El Niño), 8 cold- (La Niña), and 4 neutral-phase ENSO years based on the Oceanic Niño Index. Large magnitude lightning anomalies were found during the warm phase of ENSO, with mean warm-phase anomalies of > 10 Fl (1000 km)−2 min−1 in north-central Africa and Argentina. This includes a +35 Fl (1000 km)−2 min−1 anomaly in Argentina during the 2009 El Niño. In general, large-scale anomalies of thermodynamic properties and upper atmospheric vertical motion coincided with the lightning anomalies observed in both Africa and South America. The anomaly over north-central Africa however was characterized by a 6-week shift in the annual lightning maximum with the warm phase, a result of the more complex environmental response to ENSO over the Sahel. The most consistent ENSO anomalies with appreciable lightning were found in southeastern Africa, northwestern Brazil, central Mexico, and the southern Red Sea. Of these, all but the Mexico region had enhanced lightning with the cold phase and suppressed lightning with the warm phase.

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B. J. Turner
and
G. L. Austin

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Three-dimensional radar data for three summer Florida storm are used as input to a microwave radiative transfer model. The model simulates microwave brightness observations by a 19-GHz, nadir-pointing, satellite-borne microwave radiometer.

The statistical distribution of rainfall rates for the storms studied, and therefore the optimal conversion between microwave brightness temperatures and rainfall rates, was found to be highly sensitive to the spatial resolution at which 0bservations were made. The optimum relation between the two quantities was less sensitive to the details of the vertical profile of precipitation.

Rainfall retrievals were made for a range of microwave sensor footprint sizes. From these simulations spatial sampling-error estimates were made for microwave radiometers over a range of field-of-view sizes. The necessity of matching the spatial resolution of ground truth to radiometer footprint size is emphasized. A strategy for the combined use of raingages, ground-based radar, microwave, and visible-infrared (YIS-IR) satellite sensors is discussed.

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H. G. Houghton
and
J. M. Austin

Abstract

Surface pressure changes can occur only when an accelerational field exists. The regularity of occurrence, the distribution, and the magnitudes of the accelerational fields found in the atmosphere have been determined from the available data. The most direct method used was to plot maps of the deviation of the observed wind from the geostrophic wind. Charts of the horizontal divergence, as determined from the observed winds, were prepared for several levels. Charts were also drawn of the non-geostrophic temperature changes, which are defined as the difference between the actual 12-hour temperature changes and the temperature changes which would result from geostrophic advection of the temperature field. It is shown that the magnitudes of the divergence and the non-geostrophic temperature changes are consistent with the observed deviations from the geostrophic wind. The errors of each method are investigated and it is concluded that they are not sufficient to affect the order of magnitude of the results. All of the charts exhibit definite patterns which show a considerable degree of correspondence with the weather conditions. It is concluded that accelerational fields regularly occur in the atmosphere which are one order of magnitude greater than cyclostrophic accelerations and accelerations due to the variation of the Coriolis parameter.

The equation for the pressure tendency is discussed with reference to the observational data. Since the total divergence in a vertical column is the relatively small difference between large divergences of opposite sign, the divergence integral in the tendency equation apparently cannot be evaluated from the data. Furthermore the sum of the divergence and advective integrals yield only the surface pressure tendency, which is already available. It does not appear that the divergence can be prognosticated as accurately as the pressure field. It is pointed out that the vertical velocities associated with a field of divergence may cause large pressure and temperature changes aloft with no surface pressure change. This shows that it is not possible to determine the regions responsible for surface pressure changes by considering the changes in the several layers. The influence of vertical stability on surface pressure changes was investigated statistically with indeterminate results.

A model of a cyclonic development based on the latent heat of condensation is discussed. It appears that this mechanism is incapable of explaining pressure changes of the magnitude commonly observed. A mechanism by which additional accelerations and pressure changes might result from the deformation of the field of mass by an initial accelerational field is presented. Sufficient evidence has not been accumulated to determine whether this mechanism operates in the atmosphere.

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H. G. Houghton
and
J. M. Austin

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Kenneth J. Voss
and
Roswell W. Austin

Abstract

Transmissometers always accept a certain portion of the forward-scattered light. The error in the beam-attenuation coefficient c(λ) due to this acceptance varies with the small-angle scattering function, single-scattering albedo, and instrumental design. This paper details methods to model error in measurements of c(λ) obtained with cylindrically limited and collimated-beam transmissometers. These models are used with real examples of beam attenuation and small-angle scattering function data to test how this measurement error varies.

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J. M. Austin
and
R. Shapiro

Abstract

The hypothesis is investigated that there is a physical difference between the development and motion components of a surface pressure change. Temperature changes indicate that deepening and filling are accompanied by high-level heating and cooling, respectively, while the motion part of pressure changes is associated with low-level temperature variations.

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