From: Qixu Mo (qmo at arc.ias.sdsmt.edu)
Organization: SDSMT
Research Area: WEATHER DYNAMICS
Mission Scenario: Electric Field Inside Thunderstorms
In situ measurement of electric field inside thunderstorms is important
for us to understand their electrical activities. Over 50 years,
most in situ measurement was made with balloons and airplanes and a few
were made with rockets. Because of thunderstorm's complexity and the large
volume of air involved, none of these previous measurement has given us
adequate information we need to understand the electrification processes.
A free balloon rising through a cloud can provide a vertical profile of
the electric field, but the data in the profile are taken in a period of
20 to 30 minutes (time it takes a balloon to rise from ground to cloud top).
During this time, many electrical events ( for example, lightning flashes,
Charge has increased, decreased or moved) may have happened that the
Profile is not a representation at a certain time instant. It would be ideal
to have each balloon finish the electric field sounding from ground to cloud
top in 1 or 2 minutes and have many balloons (deployed in an array, balloon
to balloon distance less than 3 km) to be launched simultaneously through a
thundercloud, but this is impossible. Airplanes can measure electric field
in a wide horizontal extend, but few instrumented airplanes are available
for getting multiple airplane penetration of the same cloud to map the
electric field every one or two minutes. With HIAPER, quick mappings of
the thunderstorm charge distribution and the evolution may be obtained.
HIAPER Mission: HIAPER should be able to carry 5 to 20 dropsondes
for electric field measurement. During a field operation, the dropsondes
are dropped from the cloud top into the thunderstorm at several positions
as determined from radar reflectivity contours or by lightning mapping
data. Dropsondes are released at a separation of 10 to 20 seconds in time
and about 2 to 3 km in horizontal distance. In this way many samples of
the vertical profile at various positions of the whole thunderstorm
can be obtained in a short time. With more dropsondes, a variety of
experiment can the designed to help our understanding thunderstorm
charge distribution and the electrical activities.
Measuring Anvil Electric Field:
Anvil cloud often contain layers of electric charge. It is believed some
positive charge comes from the main cloud from which the anvil develops;
but the negative charges are either blown out from the main cloud and/or
from the screening layer charges. There has been a few measurement of the
anvil electric field by airplane and by vertical ascending balloons.
More observation in the horizontal variation of the electric charge
distribution are needed to understand the anvil charge origin.
HIAPER mission: Equip HIAPER with electric field meters for measuring
all three electric field components. Fly HIAPER above,below and through
the anvil to measure the horizontal variations of the E-field to find
the horizontal variation in the electric charge distribution. These
data will help to find: (1) How charges are distributed in the anvil,
(2) how often the screening layers are formed at top or bottom of the
anvil, (3)how screening layer charges at top of anvil sediment down
into the anvil cloud, (4) if and how negative charge come from the
convection region ?
E-field above thundercloud in relation with Sprites and blue jets:
Sprites and blue jets above thunderstorms are found to be associated
with the positive CG lightning discharge, but the initiation mechanism
of these phenomena is still unknown. As proposed by Boccippio et al,
Observation of E-field or E-field changes above the thunderstorms may
provide an way towards understanding the mechanisms. For this purpose,
a set of electric field meters should be installed on HIAPER to measure
the electric field above the thundercloud.
HIAPER mission: fly HIAPER over a MCS stratiform region for the life of
the storm to record Electric field, the field changes, the Sprite and
blue jet. The data then can be studied in context with the lightning
detection data and the radio signal emitted from the lightning strikes.
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