Influence of Energetic Electron
Precipitation (EEP)
on the Atmosphere
Cora Randall
University of Colorado
Department of Atmospheric & Oceanic Sciences (ATOC)
Laboratory for Atmospheric & Space Physics (LASP)
Cora Randall, SORCE meeting, September 2012
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Outline
Introduction
WACCM simulations of auroral electron precipitation
─ Composition
─ Temperature
─ Wind
Conclusion
Acknowledgments
Charley Jackman, Lynn Harvey, Ethan Peck, Laura Holt, Matthias
Brakebusch, Susanne Benze
NCAR WACCM group, Satellite instrument teams
NASA LWS, NSF CEDAR, NSF FESD
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To what extent are EEP effects
indicative of, and to what extent
do they trigger,
Atmospheric Coupling?
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Premise:
EEP-induced changes
in polar ozone trigger a
redistribution of solar
and magnetospheric
energy at Earth.
Analogous to changes
in ozone gradients
induced by solar
irradiance
O3
Waves
Temp
Winds
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Energetic Particle Precipitation (EPP)
Medium & High
Energy Electrons
Solar Protons
Adapted from
Lean, 1994
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Energetic
Particle Precipitation
(EPP)
↓↓↓
e-
e-
Direct Effect
Indirect
Effect
thermosphere
Ionization &
Dissociation
NO
↓↓↓
mesosphere
NOx and HOx
NO
NOx and HOx
Destroy Ozone
x
O3one
stratosphere
NO
O 3one
troposphere
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Requires efficient downward transport during
polar night
Odd nitrogen lifetime in
sunlight:
70-80 km: Days
50-60 km: Weeks
<40 km: Months-Years
V. Lynn Harvey
INDIRECT EFFECT
Influenced by Dynamics
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First satellite observations of EPP Indirect
Effect from LIMS in NH, 1978-1979
Many observations
of EPP IE in last
couple decades
EPP-NOx ~10% (up
to 40%) of NOx in
global (polar)
stratosphere
EPP-NOx increases
associated with O3
decreases
Cause/effect and
other impacts?
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Whole Atmosphere Community Climate Model
A 3D coupled chemistry climate model
0 to ~145 km
Comprehensive chemistry incl. heterogeneous rx
Interactive Chemistry or Specified Meteorology
1-1.5 km vertical resolution in stratosphere
1.9 x 2.5 horizontal resolution
Ref: Garcia et al., 2007
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WACCM Parameterization of Precipitation Effects
Aurora
Solar Proton Events
Input = Kp
Distribution = Auroral Oval
Roble and Ridley, 1987
Input = GOES proton flux
Distribution = polar cap
Jackman et al., 2008
Medium Energy Electrons (30 keV – 1 MeV)
Input = MEPED electron flux
Distribution = Codrescu patterns (JGR, 1997)
Fang et al., 2008
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Three WACCM Simulations
● 42 years, perpetual (annually repeating)
● Seasonally varying input except Kp
● f10.7 = 210 (solar max)
High Aurora (HA): Kp = 4 (Ap = 27)
Low Aurora (LA): Kp = 2/3 (Ap = 4)
Control: Same as LA, but new initial conditions
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~Altitude (km)
WACCM HA NOx similar to MIPAS in SH 2003 (Ap=23)
Less NOx in mesosphere, Later descent
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Comparison of NOy with/without Aurora
Δ NOy (HA-LA), 80°N
Δ NOy (HA-LA), 80°S
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Comparison of O3 with/without Aurora
Δ O3 (HA-LA), 80°S
HOX-induced O3 loss
NOX-induced O3 loss
NOx ties up ClO
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Statistically significant effects on
stratospheric temperature occurred only in
Nov-Jan at high southern latitudes
Look more closely at WACCM results here,
starting with ozone
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HA Ozone, 80°S
Δ Ozone, 80°S
Stratospheric O3 depletion coincides with significant NOx
increase (white contour = ΔNOx, 97th percentile)
Lower stratosphere O3 increase coincides with ClONO2 increase
(black contour = ΔClONO2, 97th percentile)
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Control Δ Ozone
Pressure (hPa)
Δ Ozone, 80°S
Caution: Although small and statistically insignificant,
some "signals" in control resemble HA-LA differences
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HA Temp, 80°S
Δ Temp, 80°S
December temperature increase in lower stratosphere coincides
with O3 increase (white contour = 95th percentile) – UV heating
Cooling above 30 km also coincides with O3 increase – Dynamics
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Δ Temp, 80°S
Control Δ Temp
Caution: As for O3, some small, statistically insignificant
"signals" in control resemble HA-LA differences
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Dec Lat
Gradient
ΔT
ΔZ
ΔU
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Z Gradient, 60-80°S
Δ Z Gradient
White Contour:
ΔZ > 0 at 80°S
Black Contour:
ΔT > 0 at 80°S
Zonal Wind, 70°S
Δ Zonal Wind, 70°S
White Contour:
ΔZGrad < 0 at 70°S
Zonal wind
more
easterly:
"Summer"
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Same caution as for O3 and T: Similar (but smaller and not
significant) signals in control.
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Shift to summer
wind conditions
↓
Ascent
(Δwbar* > 0, black)
↓
Cooling
O3 increase (white)
caused by upward
transport.
Cooling in mesophere: Implications
for polar mesospheric clouds
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Δ Temperature, 80°S
Control Δ Temperature
Control results again suggest
caution with interpretation.
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Does auroral EEP cause Coupling?
WACCM: Yes, in the SH. But:
O3
Random effects muddy
interpretation
42-yr run vs. 42 annual
runs?
WACCM: Persistent SH
vortex
Waves
Temp
Issues with WACCM
descent in mesosphere
Similar considerations for
interpreting SSI simulations.
Winds
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High Energy Particle Precipitation in the Atmosphere
SOLAR Influences for SPARC
(Stratospheric Processes And their Role in Climate)
Boulder, Colorado
NCAR/HAO
9-12 October 2012
http://www2.acd.ucar.edu/heppasolaris
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Thanks very much!
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