Search Results

You are looking at 11 - 17 of 17 items for

  • Author or Editor: R. List x
  • Refine by Access: All Content x
Clear All Modify Search
R. List
,
P. H. Schuepp
, and
R. G. J. Methot

Abstract

Calculations are presented of the relative contributions of heat exchange by conduction and convection, by evaporation, and by the supercooling of accreted drops to the total heat exchange of growing spherical hailstones. They reveal the regions of dominance of the different ratios for various icing conditions in a model cloud and in laboratory experiments. As an additional result, it can be shown that transfer ratios occurring in hail clouds can only partly be simulated in experiments at constant pressure, but a restricted imitation at constant pressure is possible. These ratios are also considered to represent new parameters for future experiments about the relationship between icing conditions and resulting hailstone shells.

Full access
R. List
,
R. B. Charlton
, and
P. I. Buttuls

Abstract

Calculations are made on the growth of hailstone embryos of given size and concentration which are injected into a one-dimensional steady-state updraft, and grow while ascending, the updraft obeying the condition that ρ Vs is a constant. The growth was found to have a considerable effect on the free water content of the cloud due to depletion by the growing particles. The hailstones of this model generally reach biggest sizes if their concentration is low and if the embryos are as big as possible. Embryos of 5 mm diameter can grow to 2.5–3.0 cm in diameter within 8–12 min if the conditions are right.

It is further shown that thermal feedback is of great importance in calculating the cloud temperature since it greatly affects buoyancy and icing conditions; in this case, the frictional heating of the falling hydrometeors has to be included along with the heat of fusion. The buoyancy is investigated because it is necessary to decide which set of input parameters for the growth curves and the free water contents distributions is reasonable. For those hailclouds where hailstones grow while ascending, it may be concluded that the biggest updrafts do not necessarily produce the biggest hailstones. The icing conditions of the growing particles turned out to be such that the outermost layers of the biggest stones always grow non-spongy.

Full access
R. List
,
K. R. Gabriel
,
B. A. Silverman
,
Z. Levin
, and
T. Karacostas

Abstract

A randomized rain enhancement experiment was carried out during 1988–94 in the area of Bari and Canosa, Italy, on the Adriatic coast. It was commissioned by the Italian Department of Agriculture and Forestry and the region of Puglia, with TECNAGRO, a nonprofit Italian company, as overall manager, and with EMS, an Israeli company, as field operator. The original purpose was to study rain-producing weather systems in southern Italy, establish similarities with Israel, and transfer Israeli technology. The experiment was a cross-over design with two alternating target areas, a buffer in between, and two additional control areas. Seeding was by injection of silver iodide into clouds by aircraft flying near the bases of clouds along predetermined tracks upwind of the target area. The experimental units were rainy days. Based on historical rain gauge data, it was estimated that 303 rainy days were required to establish a 15% rain increase at a significance level of 0.05 and 90% power.

In 1995, TECNAGRO asked the Scientific Committee for a statistical evaluation to investigate if a seeding effect could be established before the original goal of 303 seeding days was reached. The results of the analysis of the 260 available rainy days were that no discernable seeding effect could be found. This was evident from the root double ratio (RDR) and root regression ratio (RRR), which yielded RDR − 1 = −0.083 ± 0.089 and RRR − 1 = −0.004 ± 0.057, respectively (the ± sign represents the standard error of the estimate). Based on that result, it was decided to terminate the Puglia seeding experiment.

Preliminary exploratory studies suggest that the two target areas might have been affected differently by seeding and that an apparent substantial seeding effect occurred in the Bari area under conditions of moderate precipitable water between 700 and 850 mb. If these findings are confirmed by the recommended meteorological analyses and airflow studies, a new experiment with an appropriate design might be justified.

Full access
L. Machta
,
H. L. Hamilton Jr.
,
L. F. Hubert
,
R. J. List
, and
K. M. Nagler

Abstract

The primary purpose of this article is the documentation of radioactivity data collected by airborne equipment during the first of the Nevada atomic tests. While absolute magnitudes of activity are not available, the relative values are useful in checking meteorological trajectories and in making crude estimates of lateral diffusion.

Full access
Greg M. McFarquhar
,
Roland List
,
David R. Hudak
,
Robert P. Nissen
,
J. S. Dobbie
,
N. P. Tung
, and
T. S. Kang

Abstract

During the Joint Tropical Rain Experiment of the Malaysian Meteorological Service and the University of Toronto, pulsating raindrop ensembles, hereafter pulses, were observed in and around Penang Island. Using a Doppler radar on 25 October 1990, a periodic variation of precipitation aloft 30 km from the radar site, with an approximate 8-min period, was established and seemed to be caused by the evolution and motion of horizontal inhomogeneities existing within the same cell. On 30 October 1990, using a new volume scanning strategy with a repetition cycle of 3.5 min, pulsations of the same frequency were observed up to 3 km above the radar and at the ground by a disdrometer. High concentrations of large drops were followed by high concentrations of successively smaller drops at the ground. This provides observational evidence to support the recent argument for using a time-varying release of precipitation-sized particles to model observed pulsating rainfall.

Many cases of nonsteady rain from convective clouds displayed repetition periods of between 8 and 25 min.

Full access
Robert Nissen
,
Roland List
,
David Hudak
,
Greg M. McFarquhar
,
R. Paul Lawson
,
N. P. Tung
,
S. K. Soo
, and
T. S. Kang

Abstract

For nonconvective, steady light rain with rain rates <5 mm h−1 the mean Doppler velocity of raindrop spectra was found to be constant below the melting band, when the drop-free fall speed was adjusted for pressure. The Doppler radar–weighted raindrop diameters varied from case to case from 1.5 to 2.5 mm while rain rates changed from 1.2 to 2.9 mm h−1. Significant changes of advected velocity moments were observed over periods of 4 min.

These findings were corroborated by three independent systems: a Doppler radar for establishing vertical air speed and mean terminal drop speeds [using extended Velocity Azimuth Display (EVAD) analyses], a Joss–Waldvogel disdrometer at the ground, and a Particle Measuring System (PMS) 2-DP probe flown on an aircraft. These measurements were supported by data from upper-air soundings. The reason why inferred raindrop spectra do not change with height is the negligible interaction rate between raindrops at low rain rates. At low rain rates, numerical box models of drop collisions strongly support this interpretation. It was found that increasing characteristic drop diameters are correlated with increasing rain rates.

Full access
T. J. Ansell
,
P. D. Jones
,
R. J. Allan
,
D. Lister
,
D. E. Parker
,
M. Brunet
,
A. Moberg
,
J. Jacobeit
,
P. Brohan
,
N. A. Rayner
,
E. Aguilar
,
H. Alexandersson
,
M. Barriendos
,
T. Brandsma
,
N. J. Cox
,
P. M. Della-Marta
,
A. Drebs
,
D. Founda
,
F. Gerstengarbe
,
K. Hickey
,
T. Jónsson
,
J. Luterbacher
,
Ø. Nordli
,
H. Oesterle
,
M. Petrakis
,
A. Philipp
,
M. J. Rodwell
,
O. Saladie
,
J. Sigro
,
V. Slonosky
,
L. Srnec
,
V. Swail
,
A. M. García-Suárez
,
H. Tuomenvirta
,
X. Wang
,
H. Wanner
,
P. Werner
,
D. Wheeler
, and
E. Xoplaki

Abstract

The development of a daily historical European–North Atlantic mean sea level pressure dataset (EMSLP) for 1850–2003 on a 5° latitude by longitude grid is described. This product was produced using 86 continental and island stations distributed over the region 25°–70°N, 70°W–50°E blended with marine data from the International Comprehensive Ocean–Atmosphere Data Set (ICOADS). The EMSLP fields for 1850–80 are based purely on the land station data and ship observations. From 1881, the blended land and marine fields are combined with already available daily Northern Hemisphere fields. Complete coverage is obtained by employing reduced space optimal interpolation. Squared correlations (r2) indicate that EMSLP generally captures 80%–90% of daily variability represented in an existing historical mean sea level pressure product and over 90% in modern 40-yr European Centre for Medium-Range Weather Forecasts Re-Analyses (ERA-40) over most of the region. A lack of sufficient observations over Greenland and the Middle East, however, has resulted in poorer reconstructions there. Error estimates, produced as part of the reconstruction technique, flag these as regions of low confidence. It is shown that the EMSLP daily fields and associated error estimates provide a unique opportunity to examine the circulation patterns associated with extreme events across the European–North Atlantic region, such as the 2003 heat wave, in the context of historical events.

Full access