Lightning instruments
Description
Lightning is a valuable indicator for
convective activity in climatology and on
the cloud scale, and is correlated with
storm-related phenomena such as
precipitation, hail and gust. Lightning
strikes are also associated with a number of
risks to human activities. Before the advent
of satellite observations, global lightning
patterns were known only approximately.
Ground-based radio-frequency sensors provide
high-quality local measurements, but because
such sensors have a limited range, oceans
and low-population areas had been poorly
sampled. The development of space-based
lightning sensors was a major advance,
giving researchers a more complete picture
of planet-wide lightning activity.
Satellite detection of lightning is based on
the use of optical sensors that use
high-speed cameras focused on the cloud
tops. By analysing a narrow wavelength band
around 777 nm in the near-infrared region,
brief lightning flashes can be detected even
under daytime conditions. To date, satellite
lightning observations have only been made
from low-Earth orbit platforms, and have
mostly been focused on proving the science,
and on technology development. For example,
NASA’s Lightning Imaging Sensor (LIS) on the
Tropical Rainfall Measuring Mission mission,
which has been operating since 1997.
Now that lightning detection from low-Earth
orbit has been proven, a number of missions
are being planned to move monitoring an
operational basis from geostationary
platforms. This includes missions from major
meteorological agencies such as NOAA,
EUMETSAT and NSMC-CMA.
Advantages of the geostationary perspective
in lightning detection include:
− Enabling observations of a total
hemisphere with location accuracy of about
8-10 km and estimated detection efficiency
of 60-90%;
− Observation of a storm through its whole
life cycle; and
− Detection of total lightning including
cloud-to-ground and intra-cloud lightning is
detected. Intra-cloud lightning is about an
order of magnitude more frequent than
cloud-to-ground lightning.
Applications
Lightning location data are used widely in
research, as well as in various application
areas. Real-time data are used operationally
for forecast and warning services, for
example weather services, power utilities,
aviation and wildfires. While archived data
are used for applications like insurance,
climatology and other research
activities.
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Current & planned instruments
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Thunderstorms can be identified and
characterised using cloud-observing satellites
and ground radar, with cloud observing
satellites providing products with a spatial
resolution of 5 km and a sampling rate of 30
minutes, while ground radar provide spatial
resolution of 100 m – 2 km and a sampling rate
of 10-20 minutes. Lightning data can then be
layered on top of these observations to
indicate the most active parts of the storm
clouds; help narrow identification of
potentially hazardous regions; and, because of
coming real-time availability from
geostationary satellites, can be employed to
bridge gaps between successive cloud satellite
and ground radar samples.
Lightning density is also well correlated to
rainfall rates, with a high lightning rate a
reliable indicator of heavy precipitation.
This is of particular use in areas where
ground-based radar is not available or
obstructed, for example in mountainous regions
where heavy precipitation can be followed by
flash floods.
In addition to real-time and forecast
applications, the synoptic nature of satellite
lightning detection enables the tracking of
patterns over time. For example, in the
northern hemisphere, most lightning happens
during the summer months. But in equatorial
regions, lightning appears more often during
the autumn and spring. Understanding seasonal
variations such as this contributes to the
understanding lightning’s role in phenomena
such as wildfires, and could be used to
monitor changes in the climate.
Our increasing reliance on electronic devices,
both industrially and in the consumer sphere,
also increases our exposure to the risk of
lightning strike. Real-time information on
lightning activity can be a valuable tool for
the management of large-scale electrical
utilities and grids, allowing operators to
optimise operations and minimise the potential
for damage by rerouting operations.
Data from space-based optical sensors
reveal the uneven distribution of worldwide
lightning strikes. Units: flashes/km2/yr.
(Credit: NASA)
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