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3. Scientific Objectives 3.1
Pollution Effects OBJECTIVE
P1: Ambient pollution PROCESS TO BE
STUDIED: Williams et al. (1999) studied the effects of cloud
condensation nuclei (CCN) concentrations on both precipitation and
lightning. They found that maximum flash rates are higher when the CCN
concentration is high, as in polluted areas.
In the Rosenfeld hypothesis, many small aerosols suppress
coalescence and precipitation allowing a deep mixed phase region to
develop in the cloud (Rosenfeld and Lensky 1998). Charge separation and cloud electrification occur in this mixed
phase region (Williams et al.). In
their study, Williams et al. found that on high CCN concentration days,
the convection was characterized by isolated thunderstorms, strong mixed
phase reflectivity, frequent lightning, and higher surface air
temperatures. During the
low CCN concentration days, the convection was characterized by
widespread cloudiness, persistent precipitation, weak mixed phase
reflectivity, infrequent lightning, and reduced surface air
temperatures. According to
theory, increased aerosol (pollutant) concentrations over land and urban
areas lead to a stronger local electric field (MacGorman and Rust 1998,
pp. 32-35). GOALS OF STUDY:
The goal of this study is to collect aerosol concentrations,
reflectivity, and electrical data sets of storms over the domain of
interest. Areas of interest include both ‘polluted’ (high CCN) and
‘clean’ (low CCN) boundary layer air masses that are ingested into
the updrafts of storms. The data sets will be used to aid in determining the effect
pollution has on storm structure and electrical characteristics. MEASUREMENT
REQUIREMENTS: The electrical data set will be composed of lightning data
obtained from the National Lightning Detection
Network (NLDN), lightning mapping system, and electrical field
measurements obtained from balloon soundings. A three-dimensional data
set of electrical characteristics will be collected by the lightning
mapping system. The
reflectivity of the mixed phase region will be collected using CSU-CHILL
and NCAR S-Pol polarimetric radars. The WSR-88D at KHGX can be used when
available. Cloud condensation nuclei concentrations will be measured in-situ
by surface stations and balloon soundings.
The surface stations will include the Texas Natural Resource
Conservation Commission (TNRCC) sites and HEAT mesonet sites. The
University of Wyoming’s King Air Research Aircraft (UWKA) will be used
to measure sub-cloud layer aerosol concentrations and characteristics. OBJECTIVE
P2: Cloud droplet spectra PROCESS TO BE
STUDIED: The Rosenfeld hypothesis is the theory that when the
boundary layer is ‘dirty’, or polluted, the available liquid water
in the storm updraft is shared between numerous droplets. This reduces
the mean droplet size and suppresses the coalescence process (Rosenfeld
and Lensky 1998;Williams
et al. 1999). Rosenfeld
(2000)
found that aerosols from factories and power plants were dividing the
water in the clouds into droplets too small to precipitate.
Similar findings were made for his study of biomass burning
(Rosenfeld). Smaller
mean droplet size would further lead to reduced collision efficiency for
the droplets and a deeper mixed phase region in the cloud. The deeper
mixed phase region allows for more supercooled water in the presence of
ice, and therefore greater charge separation can occur according to
theory. GOALS OF STUDY:
The goal of this study is to collect simultaneous microphysical and
electrical data sets for storms in the vicinity of a polluted urban
area. The data sets will be analyzed to determine the relationship
of the cloud droplet spectra to the observed lightning characteristics. MEASUREMENT
REQUIREMENTS: Measurements of the cloud droplet spectra will be made
by the Weather Modification, Inc. Lear jet for both high aerosol (urban polluted) and lower aerosol
(environmental clean) storms in order to compare any differences.
The lightning data set will be obtained by the NLDN and lightning
mapping system. OBJECTIVE
P3: Supercooled liquid water PROCESS TO BE
STUDIED: In a recent study by Rosenfeld and Lensky (1998), they
found that the coalescence process in clouds over the polluted area of
Manila, Philippines was suppressed.
Later, Rosenfeld found that coalescence was suppressed
in clouds over and downwind of small aerosol pollution sources
(Rosenfeld 2000). Suppressed coalescence over polluted areas deepens the
mixed phase region of the clouds and suppresses the precipitation
allowing supercooled liquid water to exist at greater heights in the
cloud (Rosenfeld and Lensky). This
deeper mixed phase region allows for greater charge separation and cloud
electrification (Rosenfeld). GOALS OF STUDY:
The goal of this study is to collect simultaneous polarimetric,
microphysical, and electrical data sets of storms near the polluted
Houston urban environment. The
data sets will be combined to aid in determining the effects of
pollution on the microphysics of cloud structure and the electrification
processes via the Rosenfeld hypothesis.
The observed data will have a large spatial and temporal
resolution, so idealized cloud models will be utilized to provide
complete data fields to study. The numerical cloud models from SDSMT and
University of Oklahoma/National Severe Storms Laboratory, which have
parameterizations for microphysical and electrical processes, will be
used for this purpose and to test the Rosenfeld hypothesis. MEASUREMENT
REQUIREMENTS: Measurement of the supercooled liquid water content
and ice content will be made by the CSU-CHILL and the S-Pol polarimetric
radars. Electrical data
sets will be collected by the NLDN and lightning mapping system.
Simultaneous measurement of the supercooled liquid water content
and ice content will be made by the Lear jet research aircraft. 3.2
Urban Heat Island Dynamics OBJECTIVE
U1:
Urban heat island thermodynamic effect PROCESS TO BE
STUDIED: The Urban Heat Island (UHI) has been observed for many
decades in several large industrial cities. The UHI is known to alter
the thermodynamic stability in the metropolitan area, which could lead
to initiation or intensification of convection. Changnon (1978), using
data obtained from METROMEX, determined that urban effects leading to
more thunderstorm activity were generally thermodynamic in nature, as
opposed to microphysical. Braham et al. (1981) showed that a definite
higher thermal instability (higher temperatures) existed over St. Louis
compared to nearby rural areas during the METROMEX field campaign.
Braham et al. also determined that a moisture deficit existed in the
lower layers over St. Louis. Using equivalent potential temperature (qe)
to determine overall thermodynamic instability, Braham et al. showed
that observations at St. Louis indicated that the urban qe
was 2-4oC lower than in the surrounding rural areas. This
suggests that the urban area may be more thermodynamically stable than
nearby rural areas. In the case of Houston, there is reason to believe
that the moisture deficit may not be great enough to offset the thermal
instability. Houston, located along the Gulf of Mexico coast and with
many bayous traversing the urban areas, may have better access to
moisture to lessen or reverse the moisture deficit seen in other UHI
studies. GOALS OF THE STUDY:
The goal of this study is to obtain a data set of temperature and
moisture in and around the Houston Metropolitan area. This data will be
used to determine the thermodynamic instability in the region and how it
varies through time and space . From this analysis, the relationship between the
UHI thermodynamic effect and thunderstorm lightning intensity, from the
NLDN and the lightning mapping system, can be determined. MEASUREMENT REQUIREMENTS:
A surface mesonet in Houston and surrounding rural areas will record
hourly measurements of temperature, dew point, and wind velocity. Texas
Natural Resource Conservation Commission (TNRCC) surface monitoring
stations will be incorporated into the HEAT surface mesonet. Several
Tethered Atmospheric Observation Systems (TAOS) will be deployed in and
around the city to obtain vertical profiles of temperature, moisture,
and wind up to 1 km in height on a three hour interval. Due to the lack
of a NWS upper air station near Houston, a sounding station will be used
to conduct an atmospheric sounding on a twelve-hour basis. During
intensive operation periods, mobile sounding units will be deployed to
obtain measurements in specific areas of interest. These additional
measurements will augment the data set.
The NLDN and lightning mapping system will be used to gather the
necessary lightning data to compare with the above observations. OBJECTIVE
U2:
Urban heat island convergence PROCESS TO BE STUDIED:
An additional feature of UHI is an induced convergence zone over the
city. Braham et al. (1981) showed an UHI-induced convergence zone was
present over St. Louis during the METROMEX field study and contributed
to initiating and intensifying thunderstorm activity. A modeling study
conducted by Chen and Orville (1980) indicated that convergence plays an
important role in destabilizing and moistening the atmosphere, which in
turn can intensify convection. The Bornstein and Lin (2000) modeling
study revealed that a UHI-induced convergence zone initiated
thunderstorms. Both observational and modeling studies suggest that an
UHI-induced convergence zone may contribute to the enhanced lightning
activity observed in the Houston area. GOALS OF THE STUDY:
The goal of this study is to obtain horizontal wind data for the SE
Texas region. From this data set, a better understanding of the role UHI-induced
convergence plays in the initiation and/or intensification of
electrically active storms over the Houston Metropolitan area can be
obtained. MEASUREMENT REQUIREMENTS:
A surface mesonet will be deployed to record hourly measurements of
surface winds in and around the Houston area. TNRCC surface stations
will add additional measurements to the HEAT surface mesonet. Wind
profilers will be installed at specific surface sites to obtain hourly
wind flow structure in the lower atmosphere. Additionally, wind velocity
data from the balloon sounding stations can be utilized to augment the
data set from the mesonet and wind profilers.
The NLDN and lightning mapping system will be used to collect the
necessary lightning data. OBJECTIVE
U3:
Urban heat island convective updraft strength PROCESS TO BE STUDIED:
Observational studies have suggested that the UHI may increase
convective updraft strengths. From METROMEX data, Semonin (1981)
indicated a 45% increase in frequency of thunder periods at the urban
recording site as compared to the rural site. A study conducted by Huff
and Changnon (1972), which separated storms by synoptic type in the
period of 1964-68, provided evidence that air mass storms tended to
intensify over Houston. Huff and Changnon also determined from thunder
data that a maximum occurrence existed over the city. Wescott (1995)
found that city-enhanced lightning appeared to be caused by an
enhancement of convective activity as storms passed over the city. This
could suggest that meteorological conditions over an UHI produce
stronger convective currents that enhance thunderstorm electrification. GOALS OF THE STUDY:
The goal of this study is to obtain convective updraft strengths in
Houston and surrounding rural areas. The criteria that must be met for
this study are: 1) at least two convective cells propagating near the
Houston region, 2) one cell must propagate over the city of Houston
(urban cell), and 3) at least one cell must propagate through
surrounding rural areas only (rural cell).
A comparison in the change in updraft strength of the urban cell
and the rural cell can indicate if the Houston UHI enhances updraft
strengths in thunderstorms. This information can then be compared with
NLDN and lightning mapping system data recorded for these storms to
determine if any correlation exists between updraft strength and total
lightning activity. MEASUREMENT
REQUIREMENTS: During periods that meet the criteria specified above,
the NCAR S-Pol and CSU-CHILL radar will be utilized to perform
dual-Doppler measurements to map the structure of the convective cells
as they pass through the region. Using dual Doppler techniques, vertical
winds in the storm cells can be determined and then compared to
lightning frequency recorded from the NLDN and lightning mapping system. 3.3
The Effect of a Complex Coastline OBJECTIVE
C1:
Low-level convergence field associated with a complex coastline and its
effects on convective initiation PROCESS TO BE STUDIED:
McPherson (1970) performed a numerical study of the effect of a complex
coastline on the sea breeze circulation.
The irregular coastline, crudely shaped like that southeast of
Houston, TX (Galveston Bay), caused localized areas of enhanced
mesoscale convergence and upward motion along the sea breeze front.
According to these model results, the preferred location for
convective showers is in the vicinity of Houston.
Many authors (Smith 1970, Klitch et al. 1985, and Gibson and
Vonder Haar 1990) have observed (using satellite and radar measurements)
that irregular coastlines enhance convective development over convex
coastlines. However, direct
measurements of the wind field at a high spatial resolution (meso-g;
10 km) have not been taken to observe how the low-level convergence
field develops prior to sea breeze convection. GOALS OF STUDY: The goal of this study is to document, in
detail, the temporal and spatial evolution of the complex sea breeze
prior to and during thunderstorm events in the Houston, TX region.
It is important to determine if the complex coastline leads to
the initiation of more thunderstorms over the Houston vicinity as
compared to other nearby coastal areas. Both observational and model data will show if the complex
sea breeze and its associated convergence and vertical motion fields are
capable of producing significant convection that could lead to a
climatological lightning enhancement over Houston. MEASUREMENT
REQUIREMENTS:
The CSU CHILL, NCAR S-Pol, and WSR-88D KHGX radars will be used to
locate the sea breeze front on a daily basis.
KHGX will be run on clear air mode whenever possible (will be
coordinated with the NWS League City, TX) to assist in documenting the
evolution of the reflectivity fine line commonly associated with the sea
breeze front. Texas Natural
Resource Conservation Commission (TNRCC) stations (see http://www.tnrcc.state.tx.us/cgi-bin/monops/select_month?region12.gif OBJECTIVE
C2:
Sea breeze interaction with the Houston heat island PROCESS TO BE STUDIED:
The interaction of the sea breeze with the urban heat island circulation
has been successfully modeled (Yoshikado 1992, Yoshikado 1994,
Nielsen-Gammon 2000). Detailed
observational studies of this process were not found in the literature.
The daytime urban heat island can persist under the influence of
the sea breeze in the absence of significant synoptic-scale flows (Yoshikado
1994). The sea breeze front
has been found to remain over the city due to the urban heat island
effects. This may cause
convergent flow patterns to appear more frequently and clearly over
coastal cities. Yoshikado
(1994) shows maximum vertical motion occurred in his model simulation in
the convergence zone of the sea breeze and the urban heat island
circulation growing over the inland side of Tokyo, Japan around 1200 LT.
He also found that when heavily urbanized regions exceed 10 km in
width (i.e., Houston, TX), the interaction between the urban heat island
and sea breeze is significant and clearly influences the local climate. The inland advance of the sea breeze is delayed and upward
motion intensified. Yoshikado’s
(1992) results indicate that the effect of the Tokyo urban heat island
can increase the wind speed 2.3 m s-1 relative to the pure sea
breeze; Nielsen-Gammon’s model simulation revealed similar results
just southeast of Houston. The
no-city simulation conducted by Nielsen-Gammon did not develop
convection over the Houston area where the climatological lightning
enhancement is located. GOALS OF STUDY: Houston, TX is approximately 50 km inland
from the Gulf of Mexico and Galveston Bay; hence, the sea breeze should
interact with the urban heat island frequently on synoptically calm
days. The goals of this
study are to determine how often both systems interact, and when they
interact, to observe if significant convection develops where the
Houston 12-year cloud-to-ground (CG) lightning anomaly is located.
Trajectory analysis for air parcels passing over the coastal city
in Yoshikado (1992) indicates that the heat island can prevent the
dispersion of urban pollutants and delay their inland transport.
Measurements of pollution and its interaction with the complex
wind flow resulting from the urban heat island – sea breeze system
will be another important goal for this study in association with the
objectives in 3.1. MEASUREMENT REQUIREMENTS:
In coordination with objective C1, the CSU CHILL, NCAR S-Pol , and KHGX
radars will monitor and collect reflectivity data in clear air mode
during sea breeze events to trace its interaction with the city of
Houston. It will be noted
when and where significant convection (defined as cells with
reflectivity factor > 35 dBZ and lightning detected by the NLDN and
the total lightning mapping array) develops and this location relative
to the sea breeze front. The
sea breeze front and urban heat island circulation will be monitored by
surface mesonet observations, along with the radar measurements. Surface pollution will also be monitored in the mesonetwork,
and the University of Wyoming’s King Air Research Aircraft (UWKA) will
perform flight legs parallel to the sea breeze front taking pollution
concentration measurements in the sub-cloud boundary layer to observe if
any concentrated regions of pollution develop within the sea breeze –
urban heat island circulations. Pollution
CCN concentration measurements will also be taken by the MGLASS units. OBJECTIVE
C3:
Intensity of sea breeze convection PROCESS TO BE STUDIED:
Both numerical model (McPherson 1970, Nielsen-Gammon 2000) and
observational studies (Gibson and Vonder Haar 1990, Stuart et al. 2000)
have shown that the sea breeze influenced by a complex coastline
develops convection in preferred locations.
A problem that needs to be addressed is whether or not this
convection is significant enough to produce the 12-year climatological
lightning anomaly observed over Houston, TX.
Gibson and Vonder Haar show a significant portion of cloudiness
resulting from a convergent sea breeze can be classified as deep
convection (cloud top temperatures < -40°C). This
will be one of the parameters examined, along with radar and lightning
data in order to characterize the convection as strong or weak and to
see how it compares to other storm types (i.e., squall line).
GOALS OF STUDY: The goal of this study is to characterize sea
breeze convection as it develops and propagates over the Houston, TX
region. Polarimetric
radars, satellite, and lightning data for each sea breeze convective
event will be examined and compared with similar data for other types of
events (i.e., squall line) to determine the potential contribution sea
breeze convection has towards the climatological lightning anomaly. MEASUREMENT REQUIREMENTS:
The CSU CHILL and NCAR S-Pol polarimetric radars will be utilized, along
with KHGX, to gather microphysical data on the sea breeze-forced
convection. First, PPI
(plan position indicator), and then RHI (range height indicator) scans
will be taken of zones of key interest.
Standard products from KHGX and the polarimetric variables (ZDR,
LDR) measured by the CHILL and S-Pol radars can be used to diagnose the
presence and amount of frozen precipitation in a storm.
The amount of graupel is related to storm severity and lightning
production (Ahijevych et al. 2000).
Lightning data from the NLDN and lightning mapping system will be
used directly as a measure of storm intensity.
GOES-8 RSO will also be requested (see objective C1) during sea
breeze events, with the definition for deep convection being that of
Gibson and Vonder Haar (1990). The
Wyoming King Air aircraft
will also conduct flight legs through certain storm regions to obtain
precipitation particle data for comparison with the radar measurements. 3.4 Atmospheric
Chemistry OBJECTIVE A1: Transport of air pollutants by thunderstorms PROCESS TO BE STUDIED: Thunderstorms have been shown to rapidly transport planetary boundary layer (PBL) contaminants to the upper troposphere (Dickerson et al. 1987). This is significant because the chemical lifetime and range of influence of these species increases dramatically with altitude. Carbon monoxide, ozone, carbon dioxide, hydrocarbons, nitrogen oxides and aerosols are abundant in the urban environment. Observing how, both qualitatively and quantitatively, the vertical profiles of these species adjusts in and around thunderstorms will increase the understanding of chemical transport and its associated effects on tropospheric chemistry. The increase of nitrogen species' lifetimes with altitude is particularly important because of their effects on ozone production. GOALS OF STUDY: Aircraft will be the main source of data. Vertical profiles of major atmospheric constituents (CO, CO2, O3, HC, NOx (NO, NO2) and aerosols) will be taken before, during, and after thunderstorm periods over the Houston region. Also, sampling of the thunderstorm's inflow (from the PBL), anvil, and downdrafts will be conducted to characterize the transport of chemical species into and out of storms. CO2 will be used as the primary tracer of air motion through clouds based on the recommendation by Huntrieser et al. (2000). MEASUREMENT REQUIREMENTS: The University of Wyoming's King Air Research Aircraft (UWKA) and the Weather Modification, Inc. (WMI) Lear jet will conduct flight legs simultaneously during thunderstorm activity. The King Air will take chemical measurements in the thunderstorm inflow and downdrafts. The Lear jet will measure the thunderstorm's anvil. Flux calculations will be performed during the post-analysis. The King Air will conduct spiral flight patterns before and after thunderstorm activity to get a sense of the background vertical profiles of the chemical species over the Houston area. The radars (WSR-88D, NCAR S-Pol, and CSU CHILL) will be used to direct the aircraft to certain regions of the storm (inflow, downdraft, and anvil). OBJECTIVE A2:
Fraction of NOx produced by lightning versus that convectively
transported from the planetary boundary layer (PBL) in thunderstorms
PROCESS TO BE STUDIED: Reactive nitrogen oxides (NOx = NO + NO2) are key to atmospheric ozone chemistry. They are relatively abundant in the urban environment, and are produced in the lightning channels of thunderstorms (Lee et al. 1997). Hence, Houston, TX is an ideal location to study NOx chemistry since it has significant ground-level sources and a cloud-to-ground (CG) lightning enhancement associated with it. Two sources have been identified for the existence of nitrogen oxides in the upper troposphere: production by lightning and the upward transport of polluted PBL air in thunderstorms. Aircraft are also a significant source, but this estimate is well understood as compared to the previous two. During the recent field campaign EULINOX, it was found that in the average thunderstorm about 60-70% of the measured anvil-NOx was produced by lightning and about 30-40% was transported boundary layer NOx (Huntrieser et al. 2000). They obtained these estimates by subtracting the CO2/NOx correlation in the clouds without lightning from the relationship in clouds with lightning. We will employ the same tactic using CO2 as a tracer of air motion. GOALS OF STUDY: The main goal of this study is to determine the relative amounts of nitrogen oxides in and around Houston thunderstorms whose sources are lightning and convective transport. Aircraft will monitor the NOx concentrations, while the lightning mapping array (LMA) will map the total lightning in the area. The effect of elevated NOx concentrations due to thunderstorms on O3 levels in the upper troposphere will be determined. Some secondary goals include: determining the amount of NOx produced per meter of flash, per flash, and per thunderstorm (to estimate global lightning-produced NOx), intracloud (IC) versus cloud-to-ground (CG) production of NOx, NOx production rates for the different components of a flash, and the lightning-produced NOx for different storm types (isolated, squall line, supercell). MEASUREMENT REQUIREMENTS: Thunderstorm penetrations to measure chemical concentrations will be conducted by the University of Wyoming's King Air Research Aircraft (UWKA) and the Weather Modification, Inc. (WMI) Lear jet. They will observe clouds with and without lightning, and at different stages of development. The King Air will maintain measurements near the base of the storm and the Lear jet will monitor the upper levels, including the anvil. The lightning mapping array (LMA) will reveal regions of lightning activity, which will be overlaid by the aircraft routes and compared to the NOx measurements. A chemical transport model (CTM) will be run to compare with the observations and produce a more complete data set for each case. The LMA will also be used to determine flash length, and by comparison to NOx measurements, a value for the amount of NOx produced per meter of flash and per flash will be determined. The LMA and National Lightning Detection Network (NLDN) will be used to determine the amount of NOx produced per IC and CG flash. Finally, the radars (WSR-88D, NCAR S-Pol, and CSU CHILL) will be used to determine storm structure and to direct aircraft to certain storm regions (inflow, downdraft, and anvil). OBJECTIVE A3:
Comparison of different NOx sources PROCESS TO BE STUDIED: The known sources of reactive nitrogen oxide species into the troposphere include (from most to least important): fossil fuel combustion, biomass burning, soil microbial production, lightning, ammonia oxidation, and aircraft (see table 1, Huntrieser et al. 2000). There is quite a bit of uncertainty in these estimates. The relative importance of these sources on an urban scale may or may not be the same as above, especially concerning a city with a significant lightning enhancement like Houston, TX. GOALS OF STUDY: A comparison between aircraft-, lightning- and ground-emissions of NOx will be the main goal of this study. MEASUREMENT REQUIREMENTS: The amount of lightning-produced NOx over the Houston area will be estimated using the direct measurements described in the previous two objectives, while the aircraft and ground NOx emissions will be estimated from previously conducted inventories. 3.5 Lightning OJECTIVE L1: Measure the total lightning over Houston PROCESS TO BE STUDIED: Lightning occurs within clouds (IC or intracloud flashes) and between the cloud and the ground (CG or ground flashes). In the past we have only measured the CG flashes using the capability of the National Lightning Detection Network (NLDN) (e.g. Orville and Huffines, 2001). Unfortunately, this is the smaller percentage of total lightning. It leaves many questions unanswered as to the role of lightning in affecting the urban atmosphere; the distribution of IC/CG ratios over Houston and surrounding areas, and an understanding of the significance of lightning in NOx production. GOALS OF STUDY: Determine the distribution of IC and CG lightning over Houston and surrounding areas. MEASUREMENT REQUIREMENTS: A total lightning, three dimensional mapping network is required. It is proposed that a Vaisala-Global Atmospherics, Inc. total mapping system with 12 sensors of the LDAR II type, or later design, be installed in east Texas. This will provide coverage of the Houston thunderstorms and geographical areas influencing the production and dissipation of thunderstorms. OJECTIVE L2: Polarity of cloud-to-ground flashes over
Houston PROCESS TO BE STUDIED: A decrease in the percentage of positive lightning over Houston (-12%) relative to the surrounding areas has been measured based on data from the NLDN (Steiger et al., 2002). We will study the variation of the polarity on a storm-by-storm basis. GOALS OF STUDY: A comparison of the polarity of charge lowered to ground for individual storms will be performed in relation to meteorological parameters determined from aircraft and radar measurements of storms over and near Houston. MEASUREMENT REQUIREMENTS: The present capability of the NLDN is sufficient to acquire the lightning data for this objective. Aircraft, radar, and total lightning measurements, however, will be needed to supplement and provide insight to the causes of the polarity change over Houston. OJECTIVE L3: Thunderstorm electric field profiles over
Houston and non-urban environments PROCESS TO BE STUDIED: The vertical electric field in thunderstorms, given certain assumptions, can be measured to estimate the polarity structure in a thunderstorm (e.g. MacGorman and Rust, 1998; Stolzenburg et al., 1998). All previous measurements, however, of the vertical electric field have been made in non-urban environments yielding the "normal" electric field profiles. The possibility of an inverted-polarity structure in thunderstorms has recently been reported by Rust and MacGorman (2002) which suggests that electric field profiles may be different in urban environments, particularly in ones influenced by pollution. GOALS OF STUDY: We propose to measure the vertical and horizontal electric field in thunderstorms in the Houston area. MEASUREMENT REQUIREMENTS: It will be necessary to make direct measurements of the vertical electric field in thunderstorms using balloon-borne instruments. At the same time we will make electric field measurements from the Wyoming King Air aircraft to determine the horizontal homogeneity of the electric field. Total lightning mapping measurements at the same time will locate lightning flash channels with respect to the electric field soundings, both vertical and horizontal. |
