WMOD00176

• Project Name: Annual Report
• Title: Seeding Operations & Atmospheric Research, 2005 Annual Report
• Prepared By: Duncan Axisia
• Date: 12/31/2005
• Weather Modification - Doc Type: Report

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airborne CCN counter that were visibly related 10
air pollution. II was determined further that these
differences were related to the satellite retrievals.
which were validated by the aircraft
measurements. Pollution is certainly affecting
Sierra clouds and precipitation detrimentally,
Through the aircraft and satellite measurements
in SUPRECIP it has been noted that much of the
Sierra precipitation was produced by surprisingly
shallow pristine clouds_ This suggests that
pollution will act detrimentally on such clouds and
may help explain the long-term losses in Sierra
orographic precipitation.

Summary of the HEAT project

The Houston Environmental Aerosol
Thunderstorm Project (HEAT) is designed to
address the fadors responsible for the observed
enhancement in lightning frequency over
Houston. TX. An array of surface and airborne
equipment were operated during this study to
characterize the thermodynamic, environmental.
and cloud properties of the atmosphere within
and outside of the urban area. II has been
speculated that enhanced aerosol concentrations
arising from urban emissions suppress
precipitation and deepen the mixed layer within
urban douds. which may alter cloud
electrification. and possibly increase lightning
frequency .

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Figure 19 Mean annual flash density (flashes
'km2tyear) for the years 1989-2000, The Houston
metro area 1$ outlined in white, while the white box
represents the urban enhancement region (Orville et
al,.2oo1)

To address the merit of this hypothesis for the
Houston region. detailed measurements of
aerosol and doud properties were necessary.
Measurements were conducted onboard the
SOAR research aircraft with complementary
surface measurements of aerosol and cloud
properties throughout the approximately 6-week
intenSive field program. Nearly identical
instrumentation suites were used on the SOAR
Cheyenne II and at the 275 m Williams Tower on
the west side of Houston. to characterize size
distributions, size-resolved hygroscopic growth.
and cloud activation efficiency of the aerosol. The
SOAR research aircraft was equipped with
multiple wing probes for direcl measurement of
cloud droplet size distributions.

The primary goal of the Houston Environmental
Aerosol Thunderstorm (HEAT) project is to
examine the sources and causes of a 50%
enhancement of c1oud-to-ground lightning
discharges over Houston. Texas. Comparable
lightning enhancement has been observed also
over Lake Charles. Louisiana. Reaching this goal
will involve quantification of the effects of
pollution. the urban heat island. and the complex
coastline on storms and lightning characteristics
in the Houston area.

The SOAR and T AMU research team designed
flight patterns to accomplish three primary
objectives:

1. Provide additional detail of the properties of
the aerosol entering cloud base. and the size
distribution of cloud droplets in the liquid
phase region of target clouds.

2. Through flights extending beyond the
Houston urban area. statistically characterize
the differences between CCN spectra within
and outside of Houston.

3, Provide a link with the ground-based
measurements by flying spirals over the
surface site.

Airborne measurements from the SOAR
research aircraft prOvided the necessary spatial
coverage of the study region as well as the direct
in situ measurements of cloud properties. To
assess the degree to which the aerosol and CCN
properties during flight times are representative
of the region, complementary measurements
were made continuously al the surface site at the

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