Significance of Transient Luminous Events to Neutral Chemistry: Experimental Measurements

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Significance of Transient Luminous Events to
Neutral Chemistry Experimental Measurements
Craig J. Rodger Department of Physics University
of Otago Dunedin NEW ZEALAND
Annika Seppälä Earth Observation Finnish
Meteorological Institute Helsinki FINLAND
Mark A. Clilverd Physical Sciences
Division British Antarctic Survey Cambridge UNITED
KINGDOM
TLE Coupling Workshop 2008 Corte, France Session
3 (Observations Modelling) 1500-1520, 24 June
2008
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Darwin sprite from 1997.
TLE impacts upon neutral chemistry?
For some time it has been suggested that red
sprites and other Transient Luminous Events may
impact the neutral chemistry of the atmosphere -
the analogy is sometimes made to lightning
discharges which produce significant quantities
of NOx at tropospheric altitudes.
Many TLE processes are understood to produce
significant ionisation increases at high
altitudes - ions and electrons interact to
produce odd hydrogen, odd nitrogen and negative
ions. This trio can then drive ozone loss through
catalytic reaction cycles.
This has been experimentally observed during
major particle precipitation events (e.g., solar
proton events) - so what about TLE?
Mike Taylor (Utah State) observations over Med.
Sea looking over above Albania (1999).
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SPE-driven O3 losses in the Arctic
NOx
O3
Verronen et al. J. Geophys. Res., 110(A9),
doi10.1029/ 2004JA010932, 2005.
NOx concentration relative percentage changes
in O3 due to SPE. While calculated, they agree
with satellite "snap-shot" observations.
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Darwin sprite from 1997.
TLE and NOx?
More than this, TLE appear to be most common
during the nighttime due to the ionospheric
conductivity (although day time measurements are
challenging to say the least), and NOx lifetimes
are strongly dependent upon sunlight, with
sunlight destroying high-altitude NOx. NOx
produced below 50km is not destroyed by
sunlight, and so have very long lifetimes.
So during the nighttime when TLE occur there is
the potential for a buildup of NOx, due to
multiple TLE occurrences. Blue Jets might be
particularly important!
It seems likely that there will be more NOx
build-up where there is more lightning, so we can
look at locations where lightning activity is
intense check.
Mike Taylor (Utah State) observations over Med.
Sea looking over above Albania (1999).
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Big Lightning - Lots at Night
Observations of large peak current lightning from
the World Wide Lightning Location Network (WWLLN)
shows that roughly 50 occur during nighttimes.
WWLLN is biased to detecting large peak currents,
which will make a big VLF sferic. Night
favoured over day most strongly in Americas and
Africa!
Roughly 50 of WWLLN-detected CGs across the
globe occur in the nighttime sector, and hence a
lot of BIG lightning activity occurs during the
night. This may also link to sprites and other
TLE. So we look for changes in NOx linked to
lightning activity.
Taken from Lay, Jacobson, Holzworth, Rodger, and
Dowden, Local Time variation in land/ocean
lightning count rates as measured by the World
Wide Lightning Location Network, J. Geophys.
Res., 112, D13111, doi10.1029/2006JD007944, 2007.
Fig 8
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GOMOS - measuring the atmosphere
We can look at NOx (NONO2) using observations
from GOMOS (Global Ozone Monitoring by
Occultation of Stars) an instrument onboard the
ESA Envisat spacecraft. GOMOS makes up to 600
occulations a day and provides altitude profiles
of neutral gas concentrations, including
NO2! Because the observations rely upon starlight
GOMOS measurements are made during the nighttime
(when NOxNO2) - and thus are very well suited
for looking at any impacts of TLE. In order to
discriminate the lightning effect, we select
sections of the world where we expect large and
small lightning levels.
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Adapted from the LIS v1.0 Low Resolution Full
Climatology dataset.
Our Selected Lightning Regions
Likely TLE regions Mid-Western USA TLE known to
occur (WWLLN peak activity at 19 LT) Central
Africa CG, high charge moment known (WWLLN peak
18 LT) SE Asia CG, high charge moment known
(WWLLN peak 18 LT) Control region Florida high
nighttime lightning rates but dominated by large
-CG (WWLLN peak activity at 19 LT)
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Adapted from the LIS v1.0 Low Resolution Full
Climatology dataset.
Our Lightning Regions
5-years of Optical Transient Detector (OTD)
satellite data, showing average annual lightning
activity (fl. km-2 yr-1). We contrast the average
seasonal variation in lightning in each of the
above regions 2America/ America Ocean (same
longitudes) Africa/ Africa Ocean (same
longitudes) SE Asia/ SE Asia Ocean (same
longitudes) Why not use WWLLN? The DE changes
with time due to station availability (and new
stations), and this can be hard to correct for,
especially over long time periods.
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OTD - Seasonal Variation Global Lightning
Because "lightning likes land", there is a vast
difference between the seasonally varying
lightning rates over our land and ocean regions.
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OTD - Seasonal Variation Global Lightning
Particularly for the American and African
sectors, there is a factor of 500 ratio between
land and ocean, even SE Asia peaks at 100. This
is a very strong "signal" to look for in the NOx
measurements.
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GOMOS NO2 partial column 50-70km
These rarely show any significant variation
between the land and oceanic regions once the
measurement uncertainties are taken into account
Red Sprites and Giant Blue Jets for this altitude
range
bars show the measurement uncertainties at the 1
standard deviation level
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GOMOS NO2 partial column 30-50km
While we expect high TLE activity in the
Mid-West, and comparatively low activity in
Florida, these panels show very similar NO2
variation.
Blue Jets and Giant Blue Jets for this altitude
range
bars show the measurement uncertainties at the 1
standard deviation level
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GOMOS NO2 partial column 20-30km
We also do not see evidence of a significant
difference is found between land or ocean
regions, or a correlation with the average
seasonal lightning variations.
Blue Jets and Blue Starters for this altitude
range
bars show the measurement uncertainties at the 1
standard deviation level
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NO2 effects at 20-30km alt Blue Jets!
Mishin, E., Geophys. Res. Lett., 24, 1919-1922,
1997.
Modelling undertaken by Mishin 1997 indicates
that blue jet-induced NOx perturbations should be
larger at lower altitudes, and hence we have also
examined the GOMOS-observed NO2 partial column
from 2030 km altitude.
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Acknowledgements
I would like to thank the workshop organizers for
making this happen. I also want to acknowledge
the funding support from the ASIM Topical Team
funding through the European Space Agency. I
really am grateful for this!
Note
This work has been published in Geophysical
Research Letters Rodger, C. J., A. Seppälä, and
M. A. Clilverd, Significance of Transient
Luminous Events to neutral chemistry
experimental measurements, Geophys. Res. Lett.,
35, L07803, doi10.1029/2008GL033221, 2008.
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Summary Conclusions - I
The NO2 column values from GOMOS do not show
evidence for large NO2 increases above the
high-lightning land regions, or seasonal
variations which match that seen in the regional
lightning activity. We therefore conclude that
there is no significant perturbation in the
nighttime NOx levels across the altitude range
from 30-70km, inside which blue jets, giant jets
and red sprites occur. TLE occurring across this
altitude range do not appear to be significant to
the NOx chemistry of the upper stratosphere and
mesosphere on a regional scale. Modeling has
indicated that blue jet-induced NO perturbations
are larger at lower altitudes, and hence we have
also examined the GOMOS-observed NO2 partial
column from 20-30 km altitude. Again, no
significant difference is found between land or
ocean regions, or correlating with the average
seasonal lightning variations
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Summary Conclusions - II
For some time it has been argued that TLE's might
have a significant impact upon on the neutral
chemistry of the atmosphere. One likely route
would be through the production of NOx due to
TLE-ionization. Even when there is a factor of
1000 between average lightning flash rates, the
GOMOS-measured NO2 column values show no
suggestion of significant perturbations in the
nighttime measurements in the altitude range
spanning 20-70 km, within the detection levels of
the instrument. While TLE may produce local
changes in NOx around the event itself, there is
little evidence that TLE are significant to the
neutral chemistry of the middle atmosphere,
unless there is weak coupling between lighting
occurrence, positive polarity high charge moment
flashes, and overall TLE occurrence.
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Christmas morning in New Zealand. Craig enjoying
a glass of bubbles on Xmas morning in Mosgiel,
New Zealand 25 December 2007.
Thankyou! Are there any questions?