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David R. Smith

Abstract

The boundary conditions for Rotunno's numerical model which simulates tornado-like vortices are examined. In particular, the lateral boundary condition for tangential velocity and the upper boundary condition for radial and tangential velocities are considered to determine if they have any significant impact on vortex development.

The choice of the lateral boundary condition did not appear to have any real effect on the development of the vortex over the range of swirl ratios studied (0.87–2.61).

The upper boundary conditions attempt to simulate both the presence and absence of the flow-straightening baffle. The boundary condition corresponding to the baffle in place produced a distinct boundary layer in the u and v field and very strong upflow and downflow within the vortex core. When this condition is removed, there is both radial and tangential motion throughout the domain and a reduction of the vertical velocity. At small swirl ratio (S = 0.87) this boundary condition has a profound impact on the narrow vortex, producing changes in the pressure field that intensifies the vortex. At higher swirl ratio the vortex is apparently broad enough to better adjust to the changes of the upper boundary condition and, thus, experiences little change in the development of the vortex.

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G. Louis Smith
and
David R. Doelling

Abstract

The effects of the earth’s oblateness on computation of its radiation budget from satellite measurements are evaluated. For the Clouds and the Earth’s Radiant Energy System (CERES) data processing, geolocations of the measurements are computed in terms of the geodetic coordinate system. Using this system accounts for oblateness in the computed solar zenith angle and length of day. The geodetic and geocentric latitudes are equal at the equator and poles but differ by a maximum of 0.2° at 45° latitude. The area of each region and zone is affected by oblateness as compared to geocentric coordinates, decreasing from zero at the equator to 1.5% at the poles. The global area receiving solar radiation is calculated using the equatorial and polar axes. This area varies with solar declination by 0.0005. For radiation budget computations, the earth oblateness effects are shown to be small compared to error sources of measuring or modeling.

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David R. Smith
and
Fred W. Leslie

Abstract

The Purdue Regional Objective Analysis of the Mesoscale (PROAM) is a successive correction type scheme for the analysis of surface meteorological data. The scheme is subjected to a series of experiments to evaluate its performance under a variety of analysis conditions. The tests include use of a known analytic temperature distribution to quantify error bounds for the scheme. Similar experiments were conducted using actual atmospheric data. Results indicate that the multiple pass technique increases the accuracy of the analysis. Furthermore, the tests suggest appropriate values for the analysis parameters in resolving disturbances for the data set used in this investigation.

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Doyle Cook
and
David R. Smith

Forecasts issued to the public during the 10-year period 1966–75 by the National Weather Service Forecast Office, Louisville, Ky., are compared with guidance forecasts produced by the National Meteorological Center for the same location. There was little overall change in the quality of forecasts issued to the public, but the guidance forecasts have improved to the extent that they are now of a quality comparable to those issued to the Louisville public.

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Steven B. Newman
and
David R. Smith

The Third International Conference on School and Popular Meteorological and Oceanographic Education was held 14–18 July 1993 in Toronto, Ontario, Canada. This conference was attended by approximately 150 educators, meteorologists, oceanographers, and government officials representing 12 countries. The themes of this conference were the role of meteorology and oceanography in the formal science education of students in grades K-12 and the enhancement of scientific literacy of the public in order to permit individuals to make better use of products and services provided by the national environmental services and the media. Sixty formal presentations plus two poster sessions and six workshops provided information on educational programs as well as a variety of classroom activities on meteorological and oceanographic topics.

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David R. Smith
and
John T. Snow
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David R. Smith
and
Ira W. Geer
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David R. Smith
and
Joseph M. Moran

The Fifth International Conference on School and Popular Meteorological and Oceanographic Education was held 5–9 July 1999 in Ballarat and Melbourne, Australia. Conference delegates included 105 teacher educators, meteorologists, oceanographers, and science communicators representing 13 nations. Principal themes of the conference were weather and ocean studies in the primary and secondary school classroom (K–12), professional development programs for teachers in meteorology and oceanography, using the Internet for schools and public education, and communicating environmental issues to the public. Oral presentations, workshops, poster sessions, and hands-on demonstrations provided information on programs for teacher enhancement, computer-aided instruction, and access to real-time weather information.

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John E. Zimmerman
,
Phillip J. Smith
, and
David R. Smith

Abstract

A study of the sensitivity of a weak winter extratropical cyclone to latent heat release (LHR) is presented using 48-h simulations of the cyclone's evolution derived from three versions of the LFM model: a MOIST simulation in which full model physics was employed, a DRY simulation in which all latent heating was removed, and a DOUBLE MOIST simulation in which the effect of latent heating on the temperature field was doubled. Results indicate that a deepening cyclone occurs in the DOUBLE MOIST simulation, a near steady-state cyclone in the MOIST simulation, and a filling cyclone in the DRY simulation. Thus, for this case the presence and intensity of LHR is of critical importance to this cyclone's intensification. In addition, using height tendency diagnoses, it is concluded that for this case in the lower troposphere the dominant LHR influence is direct, through the explicit diabatic heating forcing in the height tendency equation. In contrast, in the middle and upper troposphere this direct LHR role is no longer dominant, but rather shares its importance with the indirect effect, represented by the influence of LHR on the dynamical forcing mechanisms.

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Biao Chen
,
Shawn R. Smith
, and
David H. Bromwich

Abstract

A case study investigation into the meridional and horizontal circulation over the South Pacific Ocean is presented for the 1986–89 El Niño–Southern Oscillation (ENSO) cycle. Using the European Centre for Medium-Range Weather Forecasts (ECMWF) analyses, annual average fields are created for the years before and after the 1987 minimum (warm phase) and 1989 maximum (cold phase) in the Southern Oscillation index. The analyses reveal a shift in the split jet stream over the south Pacific sector(180°–120°W)from a strong subtropical jet (STJ) and weak polar front jet (PFJ) during the warm phase to a weak STJ and strong PFJ during the cold phase.

Analysis of the momentum budget reveals how the split jet in the upper troposphere over South Pacific Ocean evolved during the 1986–89 ENSO cycle. During the warm phase, the strong STJ is associated with advection of the mean flow momentum flux from the Australian sector, which is approximately balanced by a large negative ageostrophic term; the PFJ is primarily associated with eddy momentum convergence, which is partially counterbalanced by the ageostrophic term. During the cold phase, the weakened STJ is related to an increasingly negative ageostrophic term and a less positive mean flow momentum convergence. The strengthened PFJ is associated with an increase in the convergence of eddy momentum flux that is mainly composed of 2.5–6-day poleward momentum transport from midlatitudes and 7–30-day equatorward momentum transport from high latitudes. In general, the impacts of eddy stress on the STJ and the mean momentum divergence on the PFJ in this sector are small.

The variations in the split jet may reflect the poleward propagation of the ENSO signal via the South Pacific convergence zone. The implications for the high southern latitudes are discussed as interannual variations are found in the low-level easterlies near Antarctica and the Amundsen Sea low.

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